Materials and methods

Field observations, collection, and macromorphological description. Field observations and collection of herbarium vouchers took place on 8 September 2023 and 8 April 2024. Herbarium vouchers included living culm leaves, branches with foliage leaves, and branches with pseudospikelets, which were measured using a centimeter scale ruler in the herbarium after drying; culms and rhizomes were photographed and measured in the field using a ruler and flexible measuring tape with centimeter scale. Photographs taken in the field were deposited in an Iowa State University DataShare Repository and available at https://doi.org/10.25380/iastate.27287805. Descriptive terminology for macromorphological characters primarily followed that of ^{Judziewicz et al. (1999)}. Pseudospikelets were described using the terminology of ^{Londoño & Ruiz-Sanchez (2024)}, with structures labeled “glumes” by ^{Judziewicz et al. (1999)} termed “sterile lemmas”. “Clusters” of pseudospikelets referred to the number of pseudospikelets in a branching group. Measurement, description, and location of additional Guadua species referenced specimens from IBUG, IEB, ISC, MEXU, and US (^{Thiers 2024}), with additional reference to descriptions from ^{Presl (1830)}, ^{Fournier & Bescherelle (1886)}, ^{Swallen (1938)}, ^{Clark & Londoño (1991)}, ^{Londoño & Ruiz-Sanchez (2014)}, and ^{Ruiz-Sanchez et al. (2015}, ²⁰²⁴⁾. Descriptions of G. amplexifolia were limited to specimens collected in Mexico and Central America.

In April 2024 we collected fresh foliage leaves from the only eight individuals that comprised the population. Every individual was separated from each other for a few meters. The foliage leaf samples were kept in silica gel until processing in the laboratory.

Scanning Electron Microscopy. We used scanning electron microscopy to observe and describe the foliage leaf, lemma, and palea micromorphology of the new species. Foliage leaf and floral bract samples were obtained from E.K. McMurchie & E. Ruiz-Sanchez 1681 and prepared and imaged following a slightly modified version of the procedure of ^{McMurchie et al. (2022)}. The modifications to this procedure comprised the following: foliage leaf and floral bract samples were submerged in xylene three times to remove epicuticular wax, iridium was used to sputter coat samples, and floral bracts were flattened under weights following xylene treatment so that the abaxial surface was presented for imaging. Samples were imaged at the Iowa State University Roy J. Carver High Resolution Microscopy Facility using a Hitachi SU4800 FE_SEM field emission scanning microscope and deposited in an Iowa State University DataShare repository available at https://doi.org/10.25380/iastate.27287805. Foliage leaf and floral bract morphology were described using the terminology of ^{Ellis (1979)}, although silica bodies that ^{Ellis (1979)} described as “dumb-bell shaped” and “elliptical” were described as “bilobate” and “rondel-shaped”, respectively, in keeping with the International Code for Phytolith Nomenclature (^{ICPT 2019}), and “nodular” silica bodies were described following ^{Cunha-Santana (2017)}. Due to difficulty in observing the costal and intercostal zones of the lemma and palea, the differences between these zones were not described.

Conservation assessment and map. The conservation assessment, including calculation of area of occupancy (AOO), followed the guidelines of the International Union for Conservation of Nature (^{IUCN 2012}, ²⁰¹⁸, ²⁰²⁴). With only one known population of this species, there were too few collections to estimate the extent of occurrence (EOO). The geographic distribution map was elaborated using QGIS v. 2.16.3 (^{QGIS 2016}) and base map was provided by INEGI (https://www.inegi.org.mx/app/geo2/elevacionesmex/).

DNA extraction and SSR genotyping. DNA was isolated using the CTAB method (^{Doyle & Doyle 1987}), modified by ^{Cota-Sánchez et al. (2006)}, from 100 mg of dry leaf tissue preserved in silica gel. Plant tissue was pulverized using a TissueLyser LT (QIAGEN, Hilden, Germany). The DNA was dissolved in 100 µL in Tris EDTA buffer solution (TE). DNA concentration and the purity were measured using a NanoDrop 2000TM Spectrophotometer (Thermo Fisher Scientific, Wilmington, DE, USA). We amplified six SSR loci: one developed for Aulonemia aristulata (Döll) McClure (Aar12) (^{Abreu et al. 2011}), one developed for Guadua angustifolia (FJ476075) (^{MERPDC et al. 2009}), and four developed for G. chacoensis (Rojas Acosta) Londoño & P.M. Peterson (Gcha01, Gcha04, Gcha07 and Gcha13) (^{Rossarolla et al. 2020}).

The volume of each amplified sample was 5.5 µl containing 0.5 µl of each primer (10 µM). The forward primer was labeled with the fluorescent dyes FAM^TM (Aar12, FJ476075, Gcha07, Gcha13), HEX^TM (Gcha01, Gcha04), 2.5 µl of Multiplex PCR Kit Mix (QIAGEN Germantown, Maryland, USA), 1.5 µl of molecular grade water, and 1.0 µl of DNA. The polymerase chain reaction (PCR) was performed in an AERIS^TM thermal cycler (Esco Healthcare, Singapore) under the following conditions: initial denaturation at 95 °C for 15 min, 30 denaturation cycles, initiation step at 94 °C for 30 sec, hybridization at 54-55 °C for 1.5 min, and extension at 72 °C for 1.5 min, followed by a final extension at 72 °C for 10 min. The PCR products were assessed on a 1 % agarose gel using GelRed, visualized with a UV Transilluminator (UVP), and then analyzed in an automatic sequencer with 0.5 µl of GeneScan 500 ROX Size standard or GeneScan 500 LIZ Size Standard (Applied Biosystems, Foster City, California, USA), 9.5 µl of Formamida (Applied Biosystems) and 1.0 μL of PCR reaction mix (diluted to 1:20). The amplified products were run on a SeqStudio-232000826 (Applied Biosystems^®) to determine the allele sizes in the Laboratorio Nacional de Identificación y Caracterización Vegetal (LaniVeg, University of Guadalajara). The genotype configuration was determined using Microsatellite Analysis Software (MSA), which is a microsatellite genotyping module available on Thermo Fisher Cloud and Peak Scanner CE Fragment Sizing (Thermo Fisher^TM). The Peak Scanner module offers peak identification and fragment sizing. We infer the number of alleles as a function of the peak area for each individual and each locus.

Estimates of genetic diversity. Deviations from Hardy-Weinberg equilibrium (HWE) were evaluated for each individual across all loci and per locus in GenAlEx 6.5 (^{Peakall & Smouse 2006}). The observed heterozygosity (H_O), expected heterozygosity (H_E), allele richness (A_R), average number of alleles per locus (Na), effective number of alleles (A_e), and Wright’s fixation index (F) were obtained with SPAGeDi v. 1.3a (^{Hardy & Vekemans 2002}).

Results

Guadua lacerata Ruiz-Sanchez & McMurchie, sp. nov. (Figures 1, 2, 3).

A-F and H by E.K. McMurchie, 8 September 2023; G and I by E. ^{Ruiz-Sanchez, 24 April 2024}.

Figure 1 Guadua lacerata in the field. A. Habitat and habit. B. Mature culm leaf. C. Young culm leaf juncture of sheath and blade. D. Nodal region and bud. E. Branch thorn complement. F. Synflorescence. G. Rhizomes. H. Foliage leaves. I. Fertile florets.  

Illustration by Emma Hoover-Grinde based on McMurchie & Ruiz-Sanchez 1681 (A-G; I-J) and Ruiz-Sanchez & Perez-Garcia 816 (H; K-M).

Figure 2 Macromorphology of Guadua lacerata. A. Foliage leaf complement. B. Young culm leaf, adaxial view; B1. Closeup of culm leaf auricle; B2. Closeup of culm leaf inner ligule and adaxial blade pubescence. C. Foliage leaf ligular area. D. Pseudospikelet. E. Prophyll. F. Gemmiparous bract. G. Stamen. H. Gynoecium. I. Lemma. J. Palea. K. Posterior locidule. L-M. Anterior pair of lodicules.  

Figure 3 Micromorphology of foliage leaves and floral bracts of Guadua lacerata from McMurchie & Ruiz-Sanchez 1681. A. Foliage leaf abaxial surface. B. Foliage leaf adaxial surface. C. Lemma abaxial surface. D. Palea sulcus abaxial surface. Abbreviations: bc = bulliform cell; bi = bicellular microhair; ma = macrohair; pa = papilla; pr = prickle; sc = silica cell; st = stomatal apparatus; tri = tricellular microhair. Inset scale bars 50 μm. 

Type. Mexico. Nayarit, Santiago Ixcuintla Municipality, beside small stream between two pastures about 4.25 km northwest from Pantano Grande along Mazatlán-Tepic highway, 16 m asl, 21.8986°, -105.1659°, 8 September 2023(fl), E.K. McMurchie & E. Ruiz-Sanchez 1681 (Holotype: IBUG; Isotypes: ISC, MEXU, US).

Diagnosis. Guadua lacerata differs from all other known species of Guadua by the following combination of characters: Supra- and infranodal bands of hair conspicuous and subequal; culm leaves 19.0-27.0 cm long, the sheath 2-3 times as long as the blade, abaxially glabrous when young developing light brown hairs 0.3-0.4 mm long that fall away as the sheath dies, shredding from the base in a twisted pattern where persistent on culm; foliage leaf blades 3.2-9.0 times as long as the width, the pseudospikelets 3.4-14.7 cm long, straight to strongly falcate, somewhat laterally compressed; 6-31 fertile florets per pseudospikelet; lemmas densely pubescent, 8.4-10.8(-13.0) mm long.

Morphological description. Rhizomes pachymorph, rhizome necks short, 9-10 cm long, 9-10 cm in diameter. Culms 8-10 m tall, 4-8 cm in diam., erect and arching above, some culms slightly sinuous and forming a zig-zag pattern. Internodes 14-34 cm long, terete with sulcus running from just above bud to distal nodal line, solid or hollow, if hollow with walls of 1.6-1.8 cm thick, lumen 0.8-1 cm in diam., when young mostly dark green, yellowish where covered by culm leaves and dark brown just beneath the infranodal band, becoming darker and duller in color as the culm matures, with soft, white pubescence that is sometimes slightly matted on young culms and wears away with age. Nodes solitary, the nodal line nearly horizontal, dipping very slightly below bud, with a supranodal band ca. 1 cm wide and an infranodal band 0.8-1 cm wide, both with dense, soft, velvety white hairs, the supranodal ridge inconspicuous; bud single, triangular, the prophylls 4-5 cm long, ca. 3 cm wide, white, glabrous at the center, the margins densely pubescent with purple and light brown hairs that form vertical stripes. Culm leaves 19.0-27.0 cm long, 13.0-19.0 cm wide at the base, coriaceous when young, retaining liquid under growing sheath, becoming chartaceous with age, retained on culm from base to ca. 2 m, deciduous above; where persistent, sheath shredding from base in twisted pattern, triangular, blade and sheath easily distinguished by color at juncture; sheaths 12.7-18.5 cm long, 2-3 times as long as blade, green to yellowish green faintly mottled with yellow when young, sometimes vertically striped with purple nearer to margins, becoming light brown with age as the leaf dies, abaxially glabrous when young, developing hairs with age, hairs 0.3-0.4 mm long, soft, light brown, these later falling away as the leaf dies, adaxially glabrous and shiny, the margins densely ciliate with hairs 1.0-1.8 mm long, white to brown; auricles always present on the overlapping side of the leaf, single or very rarely double, absent or rarely present on the underlapping side, always single, 3.7-10.0 mm long on the overlapping side, 2.7-5.2 mm long on the underlapping side when present, falcate to straight, brown, densely fimbriate; fimbriae (1.5-)2.0-5.3(-12) mm long, brown abaxially, white adaxially, curved to curly; oral setae absent; outer ligules absent; inner ligules 0.8-1.0 mm long, extending the full width of the sheath, slightly arched in the center, glabrous and shiny, the margin ciliate; blades 5.8-7.2(-9.5) cm long, 6.6-8.5 cm wide at base, broadly triangular, often rounded to slightly basally constricted, sometimes splitting vertically with age, erect, persistent, green to yellowish green faintly mottled with yellow, often purplish around juncture of sheath and blade and sometimes striped vertically with purple up blade when young, turning light brown as the blade dies, the blade typically browning before the sheath; adaxially sparsely hispid along the veins, densely hispid at the base and the apex, hairs 0.5 mm long, dark brown and shiny, abaxially glabrous when young, developing hairs as the leaf matures, which later fall away as the blade dies; the margins ciliate, hairs similar to those of the sheath, 1.0-1.8 mm long, white to brown, the apex mucronate, mucro 0.5-1 mm long. Branching extravaginal, branching beginning at node 4-7(-12) aboveground, below which buds do not develop; typically consisting of a single branch per node, occasionally 2-3 branches per node in upper half of culm, primary branches in apical half frequently producing 1-3 slender, secondary branches along upper nodes; primary branches 3-5 m long, 0.8-2 cm wide; thorns absent from culm nodes; branches in basal 2 meters of culm often developing with many thorns and few leaves, apical branches with few or no thorns, the thorn complements consisting of a central thorn 1.5-2 cm long, slightly curved or recurved, and two lateral thorns 0.7-0.8 cm long, slightly curved. Foliage leaves 5-9 per complement; sheaths green, often mottled with very small yellow spots, carinate, glabrous, the margin entire; pseudopetioles 3-4 mm long, 1-1.5 mm wide, distinct, keeled, adaxially hispidulous, hairs 0.1-0.4 mm long, hyaline, abaxially glabrous or hispidulous; auricles present on one side of the sheath, 1.0-1.2 mm long, falcate to straight, green, densely fimbriate; fimbriae (1.0-)2.0-5.0(-7.0) mm long, shiny, white, straight to curly, the side without auricles developing fimbriae of the same size, color and form as those on auricles; oral setae absent; outer ligules 0.1-0.2 mm long, glabrous, truncate, the margin erose; inner ligules 0.05-0.1 mm long, glabrous, truncate, the margin minutely ciliate; blades (8.6-)13.0-16.7(-19) cm long, (1.8-)2.0-3.2(-5.2) cm wide, L : W = 3.2-9.0, 19-22 nerved, lanceolate, not tessellate, adaxially mostly glabrous, a few hyaline hairs 0.1-0.3 mm long trailing up blade from pseudopetiole, most dense at base of blade, abaxially glabrous, the base rounded, the midrib centric, visible for full length of blade, the margins cartilaginous, scabrous, the apex acute and mucronate, the mucro 0.8-2.0 mm long. Synflorescences terminating leafless or few-leaved branches on leafy culms, open, with clusters of two to three pseudospikelets with up to two orders of branching, the main axis puberulent; pseudospikelets 3.4-14.7 cm long, 4.6-4.8(-6.0) mm wide, typically falcate, sometimes straight, slightly laterally compressed, green when young, sometimes with some purple hairs, becoming brown with age, consisting of a subtending bract, a prophyll, 1 gemmiparous bract, 1 sterile lemma, 6-31 fertile florets, and a rudimentary terminal floret; subtending bracts 4-6 mm long, abaxially soft pubescent, apex with a short mucro; prophylls 3.0-3.3 mm long, abaxially soft pubescent, with ciliolate keels; gemmiparous bracts 6.0-7.0 mm long, pubescent with very short mucro; sterile lemmas 6.0-9.0 mm long, pubescent, mucronate, mucro 0.1-0.2 mm long; rachilla segments 3.5-5.0(-6.0) mm long, pubescent at the apex, the hairs white, appressed, minute and sparse at base, becoming dense and longer toward apex, 0.4-0.7 mm at rim, segments disarticulating at base of each lemma; fertile florets 6-31, with paleas typically completely enclosed within lemmas, rarely the winged keels of the palea laterally exceeding lemma by up to 0.3 mm on one side only; lemmas 8.4-10.8(-13.0) mm long, 5.9-8.0 mm wide, 15-21 nerved, ovate-lanceolate, green with faint yellow mottling and brown at apex and shoulders when young, becoming light brown with age, abaxially densely pubescent, hairs 0.1-0.2 mm long, appressed, pointing towards apex, longest on the shoulders and near apex, mostly translucent, hairs within 1 mm of lemma margin often purple, with a few purple hairs scattered throughout, these fading to brown with age; adaxially mostly glabrous, scurfy in upper 1/4, the apex with translucent hairs 0.1 mm long, the apex mucronate, the mucro (0.3-)0.4-0.5 mm long, slightly curved at the tip; paleas 6.8-8.8(-12.0) mm long, 2.5-3.4 mm wide, pale green when young, becoming stramineous to light brown with age, the apex acute, ciliate, with hairs 0.2-0.4 mm long, the sulcus 1.3-1.6 mm, 4-6 nerved, the lower 2/3 nearly glabrous with sparse hairs 0.1 mm long, the upper 1/3 with dense hairs 0.1-1.4 mm long, most dense towards apex, the enfolding margins 2-3 nerved, glabrous or mostly glabrous, sometimes with a few appressed hairs 0.1 mm long toward the apex, the keels winged, the wings 0.4-0.7 mm wide, 2-nerved, abaxially pubescent with translucent hairs 0.1-0.3 mm long, appressed, pointing toward apex, adaxially glabrous in lower 2/3, pubescent in upper 1/3 minute, appressed hairs pointing toward apex, the margins glabrous at the base the apex with cilia 0.2-0.4 mm long, one keel crossing over the other at the apex, not prolonged to prolonged 0.2 mm beyond the apex of the sulcus. Lodicules 3, lanceolate, the anterior pair 2.6-4.4 mm long, 0.5-0.7 mm wide, glabrous except for one or two hairs at the apex ca. 0.5 mm long, the posterior one 2.0-4.3 mm long, 0.4-0.5 mm wide, glabrous. Stamens 6, the anthers 3.0-5.5(-7.0) mm long, 0.8-1.5 mm wide, yellow to purple when fresh, drying yellow to light brown, basally sagittate, apically apiculate, the filaments free, 2.8-10 mm long. Ovaries 1.2-2.6 mm long, the basal part quadrangular, 0.5-1.5 mm long, 0.4-0.7 mm wide, light brown to stramineous, glabrous, the apical part blunt, 0.6-1.1 mm long, 0.6-1.0 mm wide, the style forming a hood over the apex of the ovary, typically much wider than the base but sometimes only slightly so, stramineous, densely pubescent with hairs 0.2-0.3 mm long; styles 0.6-1.0 mm long, stramineous, densely pubescent with hyaline hairs ca. 0.2-0.4 mm long, stigmas 3, plumose, white when fresh, 1.7-2.4 mm long. Caryopses when immature 11 mm long, amber; mature mature caryopses not seen.

Foliage leaf and floral bract micromorphology. Foliage leaf adaxial surface.- Long cells elongated horizontally. Bulliform cells elongated horizontally, individual cells wider than other cells in the intercostal zone. Short cells typically containing silica bodies, the silica cells alternating with long cells, occasionally occurring in files of two or three between the long cells in the costal zone. Silica bodies vertically elongated; bilobate to smooth saddle-shaped in the costal zone; bilobate, reniform, or nodular in the intercostal zone. Papillae sometimes absent; when present, surrounding stomatal apparatuses, simple, with up to eight surrounding the stomatal apparatus. Prickles absent. Microhairs in the intercostal zones, flanking bulliform cells, non-silicified, bicellular; distal cell about one and a half times as long as basal cell; basal cell parallel sided and not tapering at the base; distal cell broadly rounded at apex. Macrohairs absent. Stomatal apparatuses in one or less commonly two rows on both sides of a costal zone; subsidiary cells low dome-shaped to parallel sided.

Foliage leaf abaxial surface.- Long cells elongated horizontally. Short cells typically containing silica bodies and alternating with long cells. Silica bodies vertically elongated; bilobate to smooth saddle-shaped in the costal zone; bilobate, reniform, nodular, or rarely elongate with a smooth outline in the intercostal zone. Papillae absent. Prickles absent. Microhairs bicellular, non-silicified, scarce, located at the centers of the interstomatal region of intercostal zone and costal zone; distal cell approximately the same length as basal cells to about one and a half times as long; basal cell typically not constricted at base and nearly parallel-sided, with a slight expansion at base, less commonly constricted at base, cupule-shaped; distal cell broadly rounded to slightly tapered at apex. Macrohairs absent. Stomatal apparatus in two or more commonly three rows on both sides of a costal zone; subsidiary cells low dome-shaped to parallel sided.

Lemma abaxial surface.- Long cells elongated horizontally. Short cells, excluding silicified trichomes, typically containing silica bodies and alternating with long cells. Silica bodies rondel-shaped, cross-shaped, or vertically or horizontally elongated and bilobate or reniform in the costal and intercostal zones. Papillae abundant on long and short cells of much of lemma excluding area near margin, simple. Prickles present in both intercostal and costal zones, interspersed with macrohairs, in three to five files, frequent to infrequent on most of lemma, frequent to scarce near margin; primarily pointing toward apex; the base of the prickle small; the barb long. Microhairs including two types, non-silicified, found only near margin, apparently in intercostal zone, scarce; one type tricellular, with a basal, central, and distal cell; basal cell about twice as long as distal cell; central cell about two thirds as long as basal cell and slightly narrower than basal and distal cells; basal cell only slightly tapering at base, parallel-sided with narrow point of attachment; central cell parallel-sided; distal cell broadly rounded at apex; the other type bicellular; distal cell approximately the same length as basal cell to one and a half times as long as basal cell; basal cell about twice as long as the width, very slightly constricted at base, cupule-shaped; distal cell broadly rounded at apex. Macrohairs abundant except for near margin, where they are abundant to scarce, located in intercostal and costal zones; primarily pointing toward apex of lemma; unicellular, hard, the base of the hair swollen. Stomatal apparatuses in one to five rows near center of lemma, in one irregular row nearer to lemma margin; subsidiary cells low dome-shaped to parallel sided.

Palea abaxial surface.- Long cells elongated horizontally and about four to 20 times as long as the width. Short cells, excluding silicified trichomes, typically containing silica bodies, though nearer to margin sometimes lacking silica bodies, alternating with long cells. Silica bodies most commonly rondel-shaped or cross-shaped, occasionally horizontally elongated and bilobate, short and smooth saddle-shaped, or reniform, rarely vertically elongated and smooth saddle-shaped or rounded. Papillae absent. Prickles irregular and frequent to sparse on the enfolding margin, inner surface of the winged keel, and sulcus; pointing toward apex; the base of the prickle medium in size; the barb long. Microhairs non-silicified, including two types; one type scarce to abundant on the palea enfolding margin, abundant on the sulcus and inner surface of winged keel, tricellular with a basal, central, and distal cell; basal cell similar in size to slightly longer than the distal cell, central cell slightly shorter to about half as long and narrower than the distal cells; basal cell very slightly tapering at base and inverted cone-shaped to cupule-shaped; central cell parallel sided; distal cell slightly tapered to a rounded apex or broadly rounded at apex; the other type scarce on the palea enfolding margin and sulcus, bicellular; the distal cell similar in size to about one and a half times as long as the basal cell; the basal cell tapering at the base and cupule-shaped; the distal cell broadly rounded at apex. Macrohairs on the enfolding margin, absent in some locations and abundant in others; abundant on sulcus and inner surface of winged keel; primarily pointing toward apex; unicellular, hard, lacking specialized epidermal cells associated with base of hair; the base of the hair swollen. Stomatal apparatuses infrequent on both the palea sulcus and enfolding margin; subsidiary cells low dome-shaped.

Distribution and ecology. Santiago Ixcuintla Municipality, Nayarit, Mexico; eight clumps of culms of this species seen growing along a small, slow-moving stream between two pastures on muddy soil near several clumps of Bambusa; 16 m asl; highly disturbed habitat with some remnant tropical subdeciduous forest.

Phenology. Guadua lacerata appears to flower sporadically. At the time of collection, six culms were observed bearing flowers, one of these older and having lost most of its flowers already. At the second visit to this population, seven months after the initial visit, we saw that all the culms that flowered in September had died, with more new culms flowering. At least seven new seedlings were seen in April. It appears that only the flowering culms die off, while sterile culms remain alive.

Etymology. This species is named for the morphology of the culm leaf sheaths, which become lacerate in situ with age.

Conservation status. Guadua lacerata has been located and collected only in the state of Nayarit, Mexico, in an unprotected area between two farm fields. With the observed area covered by the plant estimated at less than about 100 m², area of occupancy (AOO) is estimated to be only 4 km² (^{IUCN 2018}), with much of this space taken up by farmland. As this species is known from only a single population and is found in an area of highly degraded habitat potentially imperiled by further development, we hypothesize that this species would be listed as Critically Endangered (CR) under criteria B2ab(iii) were a formal conservation assessment to take place (^{IUCN 2012}, ²⁰²⁴).

Notes. Vegetatively, this species most closely resembles G. amplexifolia, but differs from it in that in G. lacerata, the supranodal and infranodal bands are subequal in size, the culm leaf is only 19.0-27.0 cm long (as opposed to 22.8-45.4 cm long in G. amplexifolia), with the culm leaf sheath 2-3 times as long as the blade (as opposed to the sheath being about 1-2.5 times as the blade in G. amplexifolia), and the culm leaf sheath shreds from the base in a twisted pattern where retained on the culm as the leaf ages (Table 1). When fertile, Guadua lacerata is distinguished from all other Mexican Guadua with known inflorescences by the length and shape of its pseudospikelets, as well as the number of fertile florets per pseudospikelet. The pseudospikelets are typically falcate but sometimes straight in shape and 3.4-14.7 cm in length with 6-31 fertile florets, often exceeding the maximum pseudospikelet length and number of fertile florets of other Guadua species with similar vegetative morphology (Table 1). In contrast, the lemmas are typically shorter than those of most species of Guadua in Mexico excluding G. inermis and G. paniculata, at just 8.4-10.8(-13.0) mm long (Table 1). In addition to their shorter length, the lemmas of G. lacerata also differ from those of the morphologically similar G. amplexifolia in that they are densely pubescent (compared to the glabrous or sparsely pubescent lemmas of G. amplexifolia) (Table 1).

Additional specimens examined. Mexico. Nayarit, Santiago Ixcuintla Municipality, about 4.25 km northwest from Pantano Grande along Mazatlán-Tepic highway, 16 m asl, 21.8986°, -105.1659°, 8 April 2024 (fl), E. Ruiz-Sanchez & M.L. Perez-Garcia 816 (IBUG, IEB, MEXU).

Macromorphological key to the species of Guadua in Mexico.

1. Culms 1-3.5(-5) cm in diameter at base; supra- and infranodal bands of hair absent or inconspicuous, grayish-white; culm leaf blades deciduous........................................................................................................... 2

1. Culms 2-15 cm in diameter at base; supra- and infranodal bands of hair conspicuous, white; culm leaf blades persistent............................................................................................................................................. 4

2. Supra- and infranodal bands of hair present; culm leaf sheaths and inner ligules roughly symmetrical......................................................................................................................... G. paniculata

2. Supra- and infranodal bands of hair absent; culm leaf sheaths and inner ligules slightly to strongly asymmetrical......................................................................................................................................... 3

3. Culm internodes hollow, thin-walled; culm leaf sheaths and inner ligules strongly asymmetrical; culm leaf blades adaxially glabrous; foliage leaf pseudopetioles adaxially and abaxially hispid......................... G. longifolia

3. Culm internodes solid or hollow but thick-walled; culm leaf sheaths and inner ligules slightly asymmetrical; culm leaf blades adaxially pubescent; foliage leaf pseudopetioles adaxially and abaxially glabrous................................................................................................................................ G. guzmanii

4. Culm internodes hollow with lumen diameter at least half that of internode; culm leaves 39-69 cm long..................................................................................................................................................... 5

4. Culm internodes solid or hollow with lumen diameter less than half that of internode; culm leaves 19-46(-63) cm long................................................................................................................................................ 6

5. Culm leaf sheath to blade length ratio 5-10(-15); culm leaf auricles absent; foliage leaf pseudopetioles 4-7 mm long....................................................................................................................................... G. aculeata

5. Culm leaf sheath to blade length ratio 2.5-3.8; culm leaf auricles present; foliage leaf pseudopetioles 2-4 mm long...................................................................................................................................... G. tuxtlensis

6. Supra- and infranodal bands of hair subequal in size; culm leaves 19-27 cm long; culm leaf sheaths shredding at base with age; fertile florets 6-31 per pseudospikelet............................................................... G. lacerata

6. Supranodal band of hair narrower than infranodal band, typically about half as wide; culm leaves 23-46(-63) cm long; culm leaf sheaths not shredding at base with age; fertile florets 3-12 per pseudospikelet................... 7

7. Culm leaf sheaths densely pubescent with both dark brown hairs and minute hyaline hairs; foliage leaf pseudopetioles 2-3 mm long, adaxially pilose............................................................................... G. velutina

7. Culm leaf sheaths pubescent with light brown hairs, minute hyaline hairs present or absent; foliage leaf pseudopetioles 2-6(-11) mm long, adaxially hispidulous or glabrous............................................................ 8

8. Thorns on lower branches abundant; culm leaf auricles absent or present; pseudospikelets (3.5-)4.5-6.5 cm long; fertile florets (3-)5-12; lemmas (11.7-)13.1-17.8 cm long, glabrous to sparsely pubescent......................................................................................................................... G. amplexifolia

8. Thorns on lower branches absent or few; culm leaf auricles present; pseudospikelets 2.5-4.5 cm long, fertile florets 4-6; lemmas 5.4-10.4 cm long, pubescent......................................................................... G. inermis

Genetic diversity. We amplified eight individuals for six microsatellites. We found 30 alleles (A_R), with an average of 3.83 alleles per locus (Na); the effective number of alleles (A_e) was 2.54. The average expected heterozygosity (H_E) for the six microsatellites was 0.516 and the observed heterozygosity (H_O) was 0.506. The F (Wright’s fixation index) was 0.016.

Discussion

Among all described Guadua species, Guadua lacerata represents one of the most extreme northwesternmost in its distribution, rivaled only by the wide-ranging Guadua paniculata (^{Perez-Garcia & Ruiz-Sanchez 2023}). Two additional described species found along the Mexican Pacific coast, G. guzmanii and G. amplexifolia, are found at more southern latitudes, with G. lacerata representing the only known species of Guadua endemic to Nayarit (^{Perez-Garcia & Ruiz-Sanchez 2023}, ^{Ruiz-Sanchez et al. 2024}). Guadua lacerata appears most morphologically similar to G. amplexifolia, with fairly high morphological similarity to G. inermis and G. velutina as well (Table 1). Despite their morphological similarity, these species do not live in close proximity to G. lacerata, with the closest populations hundreds of kilometers away and G. inermis and G. velutina limited to states surrounding the Gulf of Mexico (Figure 4).

Figure 4 Geographical distribution of Guadua lacerata and morphologically similar Guadua species in Mexico. 

Although the documentation of G. lacerata appears to be the first time a Guadua larger in size than G. paniculata has been located in Nayarit, ecological modeling has previously suggested that the lowland, coastal part of the state could contain suitable habitat for several Guadua species (^{Ruiz-Sanchez et al. 2018}, ^{Ramírez-Ojeda et al. 2021}, ^{Flores-Garnica et al. 2024}). In particular, ^{Flores-Garnica et al. (2024)} found that using the environmental variables of elevation (reported as “altitude”), annual evapotranspiration, temperature annual mean, and annual precipitation, the coastal lowland of Nayarit contained areas of very good suitability for growth of G. amplexifolia and to a lesser extent G. inermis, with very small areas of half to good suitability for G. velutina. While G. lacerata bears clear morphological differences from G. amplexifolia, G. inermis, and G. velutina, the confirmation of a large, morphologically similar Guadua species in this area supports the use of these suitability estimates to locate additional Guadua populations.

The only currently known population of G. lacerata is located in an unprotected area between two farm fields, raising concerns for its continuing survival. This population is potentially threatened not only by development, but also by climate change, which is projected to shrink the potential suitable habitat of other Mexican bamboos, including G. inermis (^{Ruiz-Sanchez et al. 2018}). Systematic surveys of nearby remaining patches of forest may reveal more populations of this species, especially if targeted to nearby waterways. In the riparian species G. velutina, ^{Perez-Garcia et al. (2023)} found that waterways appeared to be the primary facilitators of gene flow, likely through seed dispersal by hydrochory. As G. lacerata appears to be similarly associated with waterways, future surveys could focus on small waterways interconnected with the stream along which the known population was located.

In contrast with other species of Guadua in Mexico, G. lacerata displayed surprisingly high apparent genetic diversity, with average expected heterozygosity for all loci, H_E, of 0.516 and observed heterozygosity, H_O, of 0.506, compared to H_E = 0.38 and H_O = 0.21 for G. amplexifolia, H_E = 0.30 and H_O = 0.20 for G. inermis, H_E = 0.33 and H_O = 0.38 for G. tuxtlensis, and H_E = 0.322 and H_O = 0.339 for G. velutina (^{Pérez-Alquicira et al. 2021}, ^{Perez-Garcia et al. 2023}). It is possible that unknown populations of G. lacerata could contribute to its relatively high genetic diversity. However, as G. inermis and G. velutina each have over a dozen known populations in Mexico, some within a few kilometers of each other, we hypothesize that the relatively high genetic diversity of G. lacerata is not due to the presence of many unknown populations but instead the unusual flowering pattern seen in this species. Guadua lacerata appears to exhibit sporadic flowering, although the timing of the flowering cycles of G. lacerata remains unknown. The term “sporadic flowering” is somewhat broad and encompasses all bamboo flowering events where only a few clumps or groups of bamboo within small area of a population of bamboo flower, regardless of whether only individual flowering clumps or entire flowering stems die, in contrast to massive synchronized monocarpy (^{Zheng et al. 2020}). In G. lacerata, the mode of sporadic flowering differs somewhat from that of the morphologically similar G. amplexifolia, G. inermis, and G. velutina in that only the flowering culms and not the entire genetic individual dies on flowering (^{Perez-Garcia & Ruiz-Sanchez 2023}). Cultivated G. angustifolia Kunth has shown a similar mode of sporadic flowering; although the flowering cycles of wild G. angustifolia remain largely unknown, they have shown slightly higher genetic diversity (H_E = 0.71 and H_O = 0.56) than that of G. lacerata (^{Posso Terranova 2011}, ^{Borah et al. 2021}, ^{Perez-Garcia & Ruiz-Sanchez 2023}). Guadua lacerata was observed to have flowering culms in both September of 2023 and April of 2024. On the second occasion in which the population was observed, young seedlings were observed and only the few culms that were seen to flower in September of the previous year had died. Pseudospikelets observed in April of 2024 appeared relatively shorter and straighter than those seen in September of 2023, while those observed in September of 2023 typically contained numerous older, brown florets near the base, possibly indicating that the pseudospikelets of this species continue to produce additional fertile florets over the growing season even as older florets develop fruits.

Among the pseudospikelets we observed in G. lacerata in September of 2023 were some of the largest and most floriferous seen in any Guadua species. The pseudospikelets of G. lacerata include the longest recorded in Mexico, exceeding those of previous record holder, G. longifolia (E.Fourn.) R.W.Pohl, which has straight pseudospikelets of about 3-10 cm long (^{Swallen 1938}). Guadua macrospiculata Londoño & L.G.Clark of the western Amazon Basin is the only known Guadua species to have pseudospikelets exceeding the length of those of G. lacerata, its pseudospikelets sometimes reaching 17 cm in length; however, G. macrospiculata has far fewer fertile florets, with a maximum number of 17 compared to the 31 seen in G. lacerata (^{Londoño & Clark 2002}).

Guadua amplexifolia has relatively few flowering records in Mexico compared to other species of Guadua, complicating comparison of this species to G. lacerata (^{Perez-Garcia & Ruiz-Sanchez 2023}). Relocation of the type population of G. amplexifolia or other potential extant populations nearby has been precluded by uncertainty surrounding its location. Tadeáš Haenke, the collector of the type material, is known to have visited both San Blas, Nayarit, and Acapulco, Guerrero, during his accompaniment of the Malaspina expedition in 1791; the type of G. amplexifolia is simply labeled “Mexico” (^{Hitchcock 1919}). Due to the uncertainty surrounding the type locality of G. amplexifolia and the observation of ^{Presl (1830)} that the culm leaves were glabrous, unlike those of more recent collections, we considered the possibility that this type material may have been collected in San Blas and represent the species we here name G. lacerata. However, ^{Presl (1830)} described G. amplexifolia as displaying glabrous, cylindrical pseudospikelets, in contrast to the densely pubescent, laterally compressed pseudospikelets that we observed in G. lacerata. Furthermore, Haenke spent only a few days in San Blas in October of 1791 due to rainy weather during the resupply visit by the Malaspina expedition; he had previously separated from the ship that visited San Blas in the spring, instead focusing on collecting inland from Acapulco (^{David et al. 2003}). In light of these findings, we believe the G. amplexifolia type to truly represent G. amplexifolia as primarily identified in Mexico and not G. lacerata.

Guadua amplexifolia is one of the most wide-ranging species of Guadua, found from southern Mexico through northern South America (^{Young & Judd 1992}). Populations of Guadua currently considered G. amplexifolia range from bamboos of modest size (e.g., Clark et al. 1144, with culms 3-6 cm in diameter and 6-7 m tall) to very large (e.g., Stevens 8606, with culms 15 cm in diameter and 15 m tall). A careful examination of morphology and population genetics of wild populations of G. amplexifolia is needed to clarify the identity of this species and whether certain populations may represent species currently undescribed. Additionally, micromorphology of foliage leaves and floral bracts may be useful for species delimitation in Guadua similar in appearance to G. amplexifolia. Foliage leaf micromorphology has been used in other Neotropical woody bamboo taxa to support taxonomic hypotheses (e.g., ^{Leandro et al. 2016}, ²⁰¹⁷), and there appear to be differences in foliar micromorphology of various Guadua species (^{Cunha-Santana 2017}, ^{Filgueira & Viana 2024}). Although only two Guadua species, G. variegata Lizarazu and G. leonardoana Afonso, L.G. Clark & P.L. Viana, have previously been described with foliar micromorphology, these two species differ from G. lacerata in several ways, including that they lack papillae on the adaxial surface and bear prickles on both leaf surfaces (^{Lizarazu et al. 2013}, ^{Afonso et al. 2023}). The micromorphology of floral bracts remains largely unstudied in Guadua, but floral and foliar micromorphology of G. amplexifolia were briefly described by ^{Montiel et al. (2006)}. In our observation of the foliar and floral micromorphology of G. lacerata, we note several features not mentioned by ^{Montiel et al. (2006)}, including papillae surrounding the adaxial stomatal complexes of foliage leaves and on the abaxial surface of the lemma. However, we considered the structures that ^{Montiel et al. 2006}) identified as operculated papillae to be silica bodies that were damaged or partially separated from the surrounding tissue, with papillae absent from the palea. As ^{Montiel et al. (2006)} limited their description of the micromorphology of G. amplexifolia to a single population from Guanacaste, Costa Rica, the micromorphology that they described may not be representative of that of G. amplexifolia of Mexico. A systematic evaluation of micromorphology of different G. amplexifolia populations in relation to morphologically similar species including G. inermis, G. velutina, and G. lacerata could supplement traditional taxonomy and molecular systematics in aiding our understanding of these species.