Introduction

The Gustavia clade is a monophyletic group of Lecythidaceae that includes only the neotropical genus Gustavia L. (^{Mori et al., 2015}; ^{Vargas and Dick, 2020}). This genus comprises small to medium sized trees (up to 30 m tall), with petiolate or sessile leaves, cauline, axillary suprafoliar or terminal inflorescences (solitary or racemose), with pedicels subtended by a single bract and two opposite or sub-opposite bracteoles inserted along the length of the pedicel (^{Prance and Mori, 1979}). The androecia of all species of Gustavia are actinomorphic, the filaments arise from the rim of the staminal tube and are much longer than those of any other neotropical Lecythidaceae. It is the only genus of the family that has apically poricidal anthers, which suggest buzz pollination (Mori and Boeke in ^{Mori, 1987}). The fruits are indehiscent and are usually globose in shape (^{Mori et al., 2015}).

The currently used infrageneric classification of Gustavia by ^{Prance and Mori (1979)} grouped the genus into three sections, based on their floral and fruit morphological differences: Hexapetala S.A. Mori, Grandibracteata S.A. Mori and Gustavia. However, additional molecular studies are required to test the monophyly of this sectional classification. Section Hexapetala is characterized by having leaf blades usually less than 30 cm, never more than 50 cm long, flowers with six calyx lobes and six petals, hypanthium with strongly developed costae persisting in the fruit, and calyx lobes with an adaxial inverted “Y shaped” thickening. Section Grandibracteata consists of monocaulous or few-branched trees, inflorescences suprafoliar, subtended by the terminal whorl of large, tightly compacted leaves, pedicels subtended by a large bract and with two large bracteoles inserted just below the hypanthium, without thickened calyx lobes and costae on the hypanthium, calyx lobes without adaxial “Y-shaped” thickenings. Members of section Gustavia comprise few-branched to many-branched trees with cauline inflorescences (axillary or suprafoliar), when suprafoliar, not subtended by a terminal whorl of large compacted leaves, pedicels subtended by a small, scale-like, usually caducous bract or normal leaves and with two variously inserted, scale-like bracteoles.

During recent botanical explorations conducted in poorly explored areas identified by ^{Ortiz et al. (2019)}, specimens of G. sessilis S.A. Mori (sect. Grandibracteata) were collected, which represent the first records of the species in Central America. This species was previously only known from two collections made in the Colombian Chocó (^{Prance and Mori, 1979}; ^{TROPICOS, 2020}). Photographs, taxonomic comments, conservation notes and a key for Central American Gustavia species are provided.

Material and Methods

Central American specimens of G. sessilis were collected in 2019 from the Darién Province (eastern Panama). Plant identifications were confirmed by comparing collected specimens with those identified earlier and housed in the University of Panama (PMA) and Missouri Botanical Garden (MO) herbaria. In addition, type specimens of G. sessilis were examined by consulting the JSTOR Global Plants database (^{Gallagher, 2010}; ^{JSTOR, 2020}).

The evaluation of its conservation status was based on the criteria of the ^{IUCN (2001)}, using the parameters of number of locations (the number of geographically or ecologically distinct areas of occurrence), extent of occurrence (criterion B1: the spatial spread of the areas currently occupied by a taxon) and area of occupancy (criterion B2: a scaled metric that represents the area of suitable habitat currently occupied by a taxon). The extent of occurrence and area of occupancy values were computed using the GeoCAT software (^{Bachman et al., 2011}), based on the information obtained from ^{Magill et al. (2020)}, ^{TROPICOS (2020)}, type specimens and the new records included in this work. The information on the morphological description of G. sessilis was obtained from ^{Mori et al. (2010 onward)}.

Results

Gustavia sessilis S.A. ^{Mori, Brittonia 28(3): 291-293. 1976}. Figs. 1, 2.

Figure 1 Gustavia sessilis S.A. Mori. Apical view of a monocaulous branch, showing the leaves forming a compact rosette, sessile oblanceolate leaf blades and a suprafoliar (terminal) inflorescence with three flowers, from Área de Manejo Especial de Bahía Piñas, Aceite, Darién, Panama. Photo credits: Orlando O. Ortiz. 

Figure 2 Gustavia sessilis S.A. Mori. Apical view of suprafoliar flower, showing its ovate petals and connate staminal ring, from Área de Manejo Especial de Bahía Piñas, Aceite, Darién, Panama. Photo credits: Orlando O. Ortiz. 

TYPE: COLOMBIA. Chocó, dense forest S of Río Condoto between Quebrada Guarapo and Mandinga, 120-180 m, 22-28.IV.1939, fl., E. P. Killip 35417 (holotype: US!, isotypes: BM!, COL!, NY!, WIS! photo).

Tree, 5 m tall, with slender trunk; leaf-bearing branches 11-14 mm diameter; leaves in a compact rosette at their apex; petiole scars touching; leaf blades sessile, oblanceolate, 71-88 × 13-15 cm, glabrous, chartaceous, with ca. 40 pairs of lateral veins; apices acuminate; margins entire; inflorescence terminal, racemose, puberulous, 4-5 flowered; rachis 45 mm long, with distinct downward-curving floral bract scars; pedicels 40-50 mm long, subtended by a single, lanceolate, parallel-veined, greenish-white bract, 75-100 × 10-25 mm, bearing directly below the hypanthium 2 oblong, acute-tipped bracteoles, 16-22 × 6-8 mm; hypanthium without costae, densely rusty-pubescent; calyx with 4 well-developed, triangular lobes, 8 × 15 mm; corolla with 8 ovate petals, rusty-white-pubescent in bud; connate androecium base 4 mm high, outermost filaments 11 mm long, anthers 3 mm long; ovary without costae, densely rusty pubescent, 6-locular, stigma 6-lobed; fruits unknown.

Vernacular name: membrillo.

Distribution and habitat: from the Chocó region of Colmbia and Bahía Piña region of Darién (Fig. 3). In Panama, this species is very common in the gallery forests of the Río Piña (Darién Province).

Figure 3 Map showing the distribution of Panamanian population of G. sessilis S.A. Mori from Área de Manejo Especial de Bahía Piñas, Aceite, Darién (triangle) and Colombian population from Río Condoto (square) and Parque Nacional Natural Utría (circle), Chocó. 

Phenology: flowers have been collected in March (Panama) and April (Colombia).

Additional specimens examined: PANAMA. Darién, Área de Manejo Especial de Bahía Piñas, Aceite, 144 m, 07°38'33''N, 78°11'06''W, 01.III.2019, O. O. Ortiz et al. 3528 (MO, PMA).

Discussion

In the Lecythidaceae monograph by ^{Prance and Mori (1979)}, eight species of Gustavia for Central America were reported, with most of them occurring in Panama. Subsequently, the taxonomic treatment for Central America by ^{Mori and Prance (2009)} only listed seven species of Gustavia, because G. verticillata Miers was not included in this work; the exact reasons or justifications for the exclusion of this species were not discussed by the authors. We have reviewed the Panamanian specimen (Duke 10964, MO) of G. verticillata cited by Prance and ^{Mori (1979)}, and it fits with the diagnostic characteristics of this species: suprafoliar inflorescences, markedly petiolate leaves and flowers with an entire calyx. Taking into account the aforementioned and our results, the flora of Central America now comprises nine species of Gustavia.

The Panamanian population of G. sessilis coincides with the morphological characteristics, habitat and ecology of the population found in the type locality in the Colombian Chocó. This species is characterized by having sessile leaves with entire margins, flower cluster without leaf-like subtending bracts, pedicels of 40-50 mm long, triangular calyx lobes and an androecial tube of 4 mm high. Gustavia sessilis is morphologically similar to G. flagellata S.A. Mori, G. grandibracteata, and G. pubescens Ruiz ex O. Berg. These four species comprise a species complex (Gustavia grandibracteata complex) characterized by having unbranched or few-branched forms, monopodial stem elongation, solitary but clustered inflorescences produced from the stem above the terminal rosette of large leaves, relatively large basal floral bracts and pedicellary bracteoles, and 4 or 6 well-defined, usually ovate or broadly ovate calyx lobes (^{Mori, 1976}). Gustavia pubescens differs from G. sessilis mainly by having leaf blades pilose abaxially and flowers with 6 petals and sepals; G. grandibracteata can be distinguished by its markedly petiolate leaves (20-78 mm long) and G. flagellata is differentiated by having leaf blades serrulate to serrate towards the apex and very widely ovate calyx lobes.

According to the IUCN Red List, this species is vulnerable VU (B1+2c) (^{WCMC, 1998}). Currently, this species is only known from three locations and comprises an extent of occurrence of 3156 km² and an area of occupancy of 12 km². Taking into account that several areas of the Chocó-Darién moist forests ecoregion are devoid of protection (^{Sarkar et al., 2009}), adding the small number of localities and the restricted natural range of this species, we recommend considering G. sessilis as an endangered species EN (B1(ii,iii,iv,v)+B2(ii,iii,iv,v)).

Key of Gustavia taxa from Central America; based on ^{Mori and Prance (2009)} with modifications