Specimen collection

We collected one specimen from each of 18 species of Melastomataceae (Table 1) for descriptions and comparisons. We chose these species aiming to sample across different ecosystems of Colombian Andes (tropical wet forest, tropical rainforest, tropical moist forest, and paramo), different clades of Melastomataceae (five out of the 11 major clades recognized by ^{Clausing and Renner (2001)}), and especially all the different growth habits known to occur in the family. Voucher specimens were identified, described, and deposited at the Herbarium of University of Antioquia (HUA); duplicate specimens were sent to the Herbarium of the Universidad Católica de Oriente (HUCO), both in Colombia.

Anatomical sample preparation

Stem portions of the fifth most apical internode were collected for analysis. The portions were fixed with FAA (10% of 40% formaldehyde, 50% of 96% ethanol, 5% of 96% acetic acid, and 35% of distilled water). Transverse, radial and tangential sections of each stem were obtained by free-hand slicing. Sections were stained with toluidine blue 0.05% and observed and photographed using a setting formed by an Olympus BH2 microscope (Olympus, Tokio, Japan), an Olympus e620 camera (Olympus, Tokio, Japan), and a NDPL-1 (2X) camera adapter (Amscope, Los Angeles, USA). This setting was located in the Palynology Laboratory of the Universidad de Antioquia, Medellín, Colombia.

Anatomical analysis

To describe the stem anatomy from the anatomical preparations we used 125 characters based on ^{Metcalfe and Chalk (1950)}, ^{Dickison (1975)}, ^{Carlquist (1985)}, ^{Wheeler et al. (1989)}, and ^{Evert (2006)}. These characters describe the epidermis (12 characters), peridermis (15), cortex in general (3), cortical parenchyma (8), cortical collenchyma (6), cortical sclerenchyma (6), vascular system in general (8), phloem (9), xylem vessels (14), xylem fibers (6), xylem axial parenchyma (6), xylem rays (9), miscellaneous xylem characters (7), pith in general (4), medullary parenchyma (8), and medullary sclerenchyma (4). The quantitative characters were the tangential diameter of solitary vessels, the number of vessels per mm², and the vessel axial length. The number of measurements per specimen were 30 for the tangential diameter of solitary vessels, 10 for the number of vessels per mm², and 20 for the vessel axial length. See the appendix for further details on these characters.

Description of growth habits

Growth habit of analyzed specimens was determined using field observations (Table 2), according to the six growth habits that we condensed from definitions in the literature (^{Eiten, 1991}; ^{Renner, 1993}; ^{Moffet, 2000}; ^{Almeda, 2001}; ^{Font-Quer, 2001}; ^{Mendoza and Ramírez, 2006}; ^{Simpson, 2006}):

Trees/shrubs: characterized by germination and growth on the ground, the presence of stem and branches with secondary growth (^{Simpson, 2006}), self-support and erect orientation (^{Font-Quer, 2001}; Figs. 1A-B).

Herbs: characterized by the thin and brittle stem, mainly unbranched, with decumbent or prostrate orientation. If present, branches are basally inserted (^{Simpson, 2006}), and, if they have an erect orientation, their height is less than two meters (^{Mendoza and Ramírez, 2006}) (Fig. 1C). Herbs show the most variable features, making it a group which is hard to define (^{Eiten, 1991}).

Lianas: exhibit a stem with initial erect orientation, when they are surrounded by abundant vegetation, they can lean or climb on a phorophyte or other object to ascend; some can develop adventitious roots on supported branches (^{Rowe and Speck, 2004}). The growth strategy of this group is similar to that of vines, differing in the vertical orientation of the liana’s stem, their self-support in early stages of development, and their thicker stems (^{Rowe and Speck, 2004}). The species of this group are also described as climbers, scandent shrubs, and creepers (^{Putz, 1984}; ^{Moffet, 2000}) (Fig. 1D).

Vines: characterized by the prostrated orientation of stem, never self-supported. Early in life, the stem creeps until it finds vertical support to grow vertically, usually developing adventitious roots (^{Moffet, 2000}; ^{Rowe and Speck, 2004}). In these plants, the principal stem is thin and flexible (Fig. 1E).

Hemiepiphytes: stem base above the ground, supported on a host plant, with roots reaching the ground (^{Moffet, 2000}; ^{Mendoza and Ramírez, 2006}). The stem base is thicker than the rest of the stem and branches, acting as the root insertion point, basally prostrated and usually erect at the branch level. The rest of the stem is short and ramified. Commonly, species identified as hemiepiphytes can grow on the ground, with stem and branches vertically oriented like a shrub (Fig. 1F).

Epiphytes: roots and adventitious roots attach to the substrate without reaching the ground (^{Moffet, 2000}; ^{Mendoza and Ramírez, 2006}), although some species can also grow on the ground (facultative epiphytes (^{Renner, 1993})) (Fig. 1G).

Statistical analyses

Group comparisons of quantitative characters (tangential diameter of solitary vessels, the number of vessels per mm², and the vessel axial length) were performed with nested ANOVAs, one for each variable, with growth habit as an independent factor, and species within growth habit as the nested factor. When group differences were significant, the Tukey test was used for multiple comparisons of groups. Due to the remarkable differences in diameter and number of vessels of Chaetolepis microphylla (Bonpl.) Miq., we repeated the analyses excluding that species. Our results were almost identical after excluding that species; therefore, we show here the analyses without it. Statistical analyses were conducted using R (^{R Core Team, 2017}).

Anatomical descriptions

Trees/shrubs

Epidermis: Trichomes are present in Graffenrieda emarginata (Ruiz & Pav.) Triana, Miconia jahnii Pittier and Miconia salicifolia Naudin only. Dendritic hairs are showed by Graffenrieda emarginata, Miconia jahnii, and Miconia salicifolia; glands are present only in the two former species. Epidermis is absent in the fifth internode of Tibouchina lepidota (Bonpl.) Baill. and Miconia salicifolia, where it is replaced by periderm. Epidermis in Meriania nobilis Triana, Graffenrieda emarginata, and Miconia jahnii is single-layered and with epicuticular wax like granules (Figs. 2A-D).

Periderm: Periderm is absent in the fifth internode of Graffenrieda emarginata and Meriania nobilis. Scaly bark is only present in Tibouchina lepidota. Periderm in Tibouchina lepidota, Miconia jahnii and Miconia salicifolia is superficial, single-layered and the formation is complete around the stem. The phellem is one- to six-layered with cells in radial disposition without intercellular spaces; the cells have pits only in Tibouchina lepidota. The phellogen is simple and one-layered. The phelloderm is one- to three-layered. Lenticels only occur in Tibouchina lepidota periderm (Figs. 2E, F).

Cortex: The cortex is mainly formed by parenchymatous cells with isodiametric shape, intercellular spaces, diverse materials, and druse accumulation (except in Tibouchina lepidota and Miconia jahnii). Photosynthetic parenchyma only occurs in Meriania nobilis cortex. The collenchyma is of the angular type, forming a continuous multiple-layered tissue around the stem inside to epidermis/periderm in Meriania nobilis, Graffenrieda emarginata, and Miconia salicifolia. Stone cells with simple and ramiform pits are found in Meriania nobilis, Graffenrieda emarginata and Miconia jahnii. In Meriania nobilis and Graffenrieda emarginata, the stone cells form a continuous three-layered tissue around the endodermis. In Miconia jahnii the stone cells form clusters ranging from endodermis to periderm. Vascular bundles compound by just xylem are only seen in Tibouchina lepidota (Figs. 2C-E, 3).

Endodermis and pericycle: The endodermis is only absent in Miconia salicifolia. In the rest of the species, the endodermis forms a continuous one- to three-layered tissue around the stem. Casparian strip is only present in Tibouchina lepidota and Miconia jahnii. The pericycle forms a continuous two- to the three-layered tissue between the endodermis and the phloem with cells in radial disposition (Figs. 4A-C).

Phloem: Sieve-tube elements are arranged in radial disposition in Meriania nobilis, Miconia jahnii and Miconia salicifolia, scattered in Tibouchina lepidota, and Graffenrieda emarginata. Sieve plates are transverse, except for Tibouchina lepidota, where they are inclined. Fibers are only present in Miconia jahnii and Miconia salicifolia; in the former, grouped in tangential bands; in the latter, forming clusters of six to eight cells located on the distal part of phloem. Axial parenchyma is composed of strands of short cells containing druses, except for Graffenrieda emarginata (Figs. 4B-E).

Vascular cambium: The vascular cambium is a one- to five-layered tissue without discontinuities, variations or irregularities; xylem and phloem form continuous tissues with constant width (Figs. 4B-D).

Xylem vessels: The vessel arrangement has radial to diagonal patterns and the grouping is in multiples of two to four with a variable proportion of solitary vessels. The outline of solitary vessels is rounded in Meriania nobilis and Miconia jahnii, and angular in Tibouchina lepidota, Graffenrieda emarginata, and Miconia salicifolia. Perforation plates are simple and inclined. Intervessel pits are rounded and bordered, have an opposite arrangement in Meriania nobilis and alternate in the other species (Fig. 5).

Xylem fibers: The fibers are of the libriform type and have transversal septa. The xylem has fiber dimorphism with two morphotypes of libriform fibers. The difference between morphotypes is in the lumen diameter and the thickness of the secondary wall. Dimorphic fibers are grouped in two to five layers formed by units that can range from short clusters to long tangential bands. The distance between dimorphic fibers is larger than the distance between rays (Figs. 5A, B, E, F).

Xylem rays: Rays are uniserial, but Tibouchina lepidota shows multiseriate portions. The cellular composition is upright and square cells. Vessel-ray pits are rounded, oval or scalariform and half-bordered, with border only in the vessel lumen (Figs. 5A, B, E-G).

Pith: The pith has internal primary phloem towards the periphery; in the center, it has parenchymatous cells with isodiametric shape and diverse materials and accumulation of druses. Vascular bundles scattered throughout the pith are concentric amphicribal of primary growth where the phloem is predominant in Miconia salicifolia, being the xylem very reduced in Graffenrieda emarginata and Miconia jahnii, and non-existent in Tibouchina lepidota and Meriania nobilis. The Miconia jahnii pith is formed largely by stone cells with a wide lumen and simple and ramiform pits. The piths of Graffenrieda emarginata are common idioblasts that are axially elongated and related to the phloem, distributed around and within the internal phloem and vascular bundles (Fig. 6).

Herbs

Epidermis: The trichomes are pluricellular; simple unbranched in Heterocentron subtriplinervium (Link & Otto) A. Braun & C.D. Bouché and Arthrostemma ciliatum Pav. ex D. Don, dendritic in Tibouchina kingii Wurdack and Chaetolepis microphylla. Trichomes of Arthrostemma ciliatum are scarce and longer than in the other species. The epidermis is absent in the fifth internode of Tibouchina kingii. The epidermis is single-layered and has an epicuticular wax with the form of granules in Heterocentron subtriplinervium and Arthrostemma ciliatum, whereas in Chaetolepis microphylla the epicuticular wax consists of short and thin filaments in perpendicular direction to the epidermis (Figs. 7A-D).

Periderm: Periderm is present only in Tibouchina kingii and Chaetolepis microphylla; in this latter species the transition where the periderm is forming below the epidermis is observed. Scaly bark is present in Tibouchina kingii only. The periderm is superficial, single-layered and the formation is complete around the stem. The phellem is two- to four-layered with cells in radial disposition. The phellogen is one-layered. The phelloderm is four- to six-layered with cells in radial disposition (Figs. 7E, F).

Cortex: The cortex is absent in the fifth internode of Tibouchina kingii, just below the phelloderm is the endodermis. In other species, the cortex is mainly formed by parenchymatous cells with isodiametric shape, with diverse materials and accumulation of druses in Heterocentron subtriplinervium and Arthrostemma ciliatum, and presence of chloroplasts in Arthrostemma ciliatum. The collenchyma is of the angular type, forming a multi-layered tissue below the epidermis in Heterocentron subtriplivernium and Chaetolepis microphylla, and in the middle of the cortex in Arthrostemma ciliatum. In Heterocentron subtriplinervium and Arthrostemma ciliatum, vascular bundles of primary growth are concentric amphicribral and those located in the stem angles are quadrangular (Figs. 7C-F, 8).

Endodermis and pericycle: The endodermis is below the cortex, it is one- to three-layered and the tangential walls have more contact area. The pericycle is a five-layered continuous tissue between the endodermis and phloem, only present in Heterocentron subtriplinervium (Figs. 8A, 9A,B).

Phloem: Sieve-tube elements are scattered in Tibouchina kingii, Heterocentron subtriplinervium, and Chaetolepis microphylla, and in radial disposition in Arthrostemma ciliatum. Sieve plates are transverse, but inclined in Tibouchina kingii. Axial parenchyma is organized in fusiform cells in Heterocentron subtriplinervium and Chaetolepis microphylla, and in a strand of short cells containing druses in Tibouchina kingii (Figs. 7E, 8B, C, 9).

Vascular cambium (procambium in Arthrostemma ciliatum): The vascular cambium is not observed in the fifth internode of Arthrostemma ciliatum, the procambium is a one-layered and simple tissue, thus the phloem and xylem are primary. In the other species, the vascular cambium is a one- to four-layered tissue without discontinuities, variations or irregularities (Figs. 8B, C, 9A-C).

Xylem vessels: Vessel arrangement has a radial to diagonal pattern, mainly solitary vessels with a little proportion of radial multiples, more common in Heterocentron subtriplinervium. The outline of solitary vessels is rounded in T. kingii and Chaetolepis microphylla, the outline is angular in Heterocentron subtriplinervium. The perforation plates are simple and inclined. Intervessel pits are rounded and bordered and have an alternate arrangement (Figs. 10A-D).

Xylem fibers: The fibers are of the libriform type and have transversal septa only in Heterocentron subtriplinervium and Arthrostemma ciliatum. Fiber dimorphism only in Tibouchina kingii and Chaetolepis microphylla. Dimorphic fibers in Tibouchina kingii are grouped in four- to six-layered tangential bands and the distance between the bands is bigger than the distance between rays. In Chaetolepis microphylla the dimorphic fibers form one tangential band of five to seven layers (Figs. 10B, E).

Xylem rays: Rays uniserial, formed by upright and square cells. Vessel-ray pits are rounded to oval and half-bordered, with a border in the vessel lumen only (Figs. 10B, F, G).

Pith: The pith has internal primary phloem towards the periphery, which is continuous in Chaetolepis microphylla and discontinuous in other species. The parenchyma is formed by cells with isodiametric shape and diverse materials and accumulation of druses. In Chaetolepis microphylla the pith is reduced and without intercellular spaces between parenchymatous cells. Vascular bundles scattered throughout the pith are concentric amphicribral of primary growth where the phloem is predominant, being the xylem very reduced in Arthrostemma ciliatum and non-existent in Tibouchina kingii. In the pith of Chaetolepis microphylla the vascular bundles are absent (Fig. 11).

Lianas

Epidermis: Trichomes have a dendritic form in Monochaetum multiflorum (Bonpl.) Naudin and Blakea fasciculata Gleason, and are absent in Blakea quadrangularis. The epidermis is single-layered, the transition with the periderm is formed below the epidermis in Blakeaquadrangularis and Blakea fasciculata. The epidermis is absent in the fifth internode of Monochaetum multiflorum. The epicuticular wax has the shape of granules (Figs. 12A-D).

Periderm: Scaly bark is present in Monochaetum multiflorum only. The periderm is superficial and single-layered. The phellem is two- to ten-layered with cells in radial disposition, without intercellular spaces and with pits (except for Blakea fasciculata). The phellogen is one- to two-layered. The phelloderm is one- to three-layered with cells in radial disposition, and is absent in Blakea fasciculata (Figs. 12D-F, 13A, 14B).

Cortex: The cortex in the fifth internode of Monochaetum multiflorum is absent, the endodermis is just below the phelloderm. In other species, the cortex is mainly formed by parenchymatous cells with isodiametric shape, diverse materials, and accumulation of druses, with chloroplasts present only in Blakea fasciculata. Collenchyma is only present in Blakea fasciculata and of the angular type, forming a five- to six-layered continuous tissue below the phelloderm, the latter containing chloroplasts and druses. The stone cells form a four-layered discontinuous tissue in the center of cortex, with simple and ramiform pits (Figs. 12D, E; 13; 14A, B).

Endodermis and pericycle: The endodermis is a continuous tissue between the cortex and the phloem. In Monochaetum multiflorum the endodermis cells show a Casparian strip with unequal thickening of cell walls and reduced lumen. In Blakea quadrangularis and Blakea fasciculata the endodermis is subtle, formed by one layer of cells larger than the cortex parenchyma cells, with thin cellular walls and without cytoplasmic accumulations. The pericycle is one- to three-layered, only present in Monochaetum multiflorum and Blakea quadrangularis; in the latter the presence of solitary fibers with thick walls, reduced lumen and simple pits is common (Figs. 12E, 13A, 14A, B; 15A).

Phloem: Sieve-tube elements scattered, with simple and transverse sieve plates. Phloem fibers present only in Blakea fasciculata, where they are scattered, mainly solitary, or rarely in clusters. Axial parenchyma in a strand of short cells with accumulation of druses, scattered in Monochaetum multiflorum and Blakea quadrangularis, and grouped in clusters in Blakea fasciculata (Figs. 13B, 14, 15A).

Vascular cambium: In the same way as trees, shrubs, and herbs, liana species show a vascular cambium lacking discontinuities, variations or irregularities that may change the vascular system conformation. The vascular cambium of Blakea fasciculata, with eight layers of cells, is the thickest among the species studied here (Figs. 14, B, 15A).

Xylem vessels: The vessel arrangement has a radial to diagonal pattern, mainly solitary in Monochaetum multiflorum and Blakea fasciculata, and more common in multiples of two to three vessels in Blakea quadrangularis. The outline of solitary vessels is rounded in Monochaetum multiflorum and angular in Blakea quadrangularis and Blakea fasciculata. Perforation plates are simple and inclined. Intervessel pits are bordered, from scalariform to opposite rounded in Monochaetum multiflorum, and alternate in Blakea quadrangularis and Blakea fasciculata(Figs. 15A, D-F).

Xylem fibers: The fibers are libriform and have transversal septa. Dimorphic fibers grouped in two- to eight-layered tangential bands, with a wider lumen and thinner walls allowing intercellular spaces. Additionally, Blakea quadrangularis xylem shows a second type of dimorphic fiber, with a narrower lumen and thicker walls, grouped in two- to six-layered tangential bands (Figs. 15A-D, G).

Xylem axial parenchyma: The axial parenchyma is of the apotracheal type, grouped in three- to six-layered clusters close to vascular cambium. This tissue is absent in Monochaetum multiflorum (Fig. 15D).

Xylem rays: Rays are uniserial, but xylem of Blakea fasciculata also shows aggregates of two to four rays, which are formed by upright and square cells. Vessel-ray pits are rounded to oval and half-bordered, with border only in vessel lumen (Figs. 15G-I).

Pith: The periphery of the pith has internal primary phloem, forming a continuous band in Blakea quadrangularis and a discontinuous one in Monochaetum multiflorum and Blakea fasciculata. In the center, the pith is formed by parenchymatous cells with isodiametric shape, diverse materials, and accumulation of druses. Vascular bundles, which are scattered throughout the pith of primary growth, are concentric amphicribral in Monochaetum multiflorum and Blakea quadrangularis, and collateral in Blakea fasciculata. The pith of Blakea quadrangularis and Blakea fasciculata also shows fibers with a narrow lumen, thick walls, and simple pits; these fibers are located around the internal phloem and the vascular bundles (Fig. 16).

Vines

Epidermis: The trichomes in Clidemia epiphytica (Triana) Cogn. are simple unbranched, whereas they are simple unbranched and dendritic in Adelobotrys adscendens Triana. The epidermis is absent in the fifth internode of Blakea granatensis Naudin. The epidermis in other species is single-layered and has an epicuticular wax in form of granules (Figs. 17A, B).

Periderm: The periderm is absent in the fifth internode of Adelobotrys adscendens, whereas in Clidemia epiphytica the transition where the periderm is forming below the epidermis is observed. The periderm is single-layered, in Blakea granatensis it is a superficial and a continuous tissue, whereas in Clidemia epiphytica it is discontinuous. The phellem is one- to eight-layered with cells in radial disposition. The phellogen is one- to two-layered. The phelloderm is one- to five-layered, with cells in radial disposition only in Clidemia epiphytica (Figs. 17C, 18A, B).

Cortex: The cortex is formed by parenchymatous cells with isodiametric shape, diverse materials, and accumulations of druses, with chloroplasts present in Adelobotrys adscendens. The collenchyma is of the angular type, forming a three- to four-layered continuous tissue below the epidermis in Adelobotrys adscendens. The stone cells form a four- to six-layered continuous tissue below the periderm in Blakea granatensis, and these have simple pits and tangential inner walls (in the direction of the pith) that are thicker than other walls (Figs. 18, 19A-C).

Endodermis and pericycle: The endodermis is a one- to two-layered continuous tissue; in Adelobotrys adscendens it is only formed by stone cells with simple and ramiform pits. The pericycle is a two- to three-layered continuous tissue; in Blakea granatensis it also consists of solitary fibers with simple pits and a narrow lumen. In Clidemia epiphytica the cells between the cortex and phloem have no variation or specialization, except that they are smaller than cortical parenchyma cells and have no cytoplasmic accumulations (Figs. 17C, 18, 19A-C).

Phloem: Sieve-tube elements are scattered in Blakea granatensis and Adelobotrys adscendens, and in clusters in Clidemia epiphytica. Sieve plates are simple and inclined, transverse in Clidemia epiphytica. Fibers are scattered in the distal part of phloem in Blakea granatensis, and form a four- to six-layered continuous tissue on the distal part of phloem in Clidemia epiphytica. Axial parenchyma is formed by a strand of short cells containing druses (Figs. 18A, 19).

Vascular cambium: The vascular cambium is a two- to four-layered tissue. In this group of species, the vascular cambium has a sinuous form that is more prominent than in other species (Figs. 18A, B, 19).

Xylem vessels: The vessel arrangement is radial to diagonal and the grouping is in multiples of two to four, with a variable proportion of solitary vessels. Vessel diameters in Blakea granatensis show a marked increase on the newly formed xylem. The outline of solitary vessels is angular. Perforation plates are simple and inclined. Intervessel pits are rounded, bordered and have an alternate arrangement (Fig. 20).

Xylem fibers: The fibers are of the libriform type and have transversal septa. The dimorphic fibers are grouped in two- to five-layered tangential bands and the distance between the bands is larger than the distance between the rays. Like Blakea quadrangularis, Adelobotrys adscendens shows two different types of dimorphic fibers (Figs. 20A-C).

Xylem axial parenchyma: Axial parenchyma is present in Blakea granatensis only, where it is the apotracheal type, grouped in four- to seven-layered tangential bands, more frequently close to the vascular cambium. The cells can be fusiform and short in their strand, showing an accumulation of druses (Figs. 18A, 19A, 20F).

Xylem rays: Rays uniserial, formed by upright and square cells. The vessel-ray pits are rounded to oval and half-bordered, with a border in the vessel lumen only (Figs. 20E-G).

Pith: The internal phloem is reduced in Adelobotrys adscendens and discontinuous in Blakea granatensis. The parenchyma cells have isodiametric shape and diverse materials and druses accumulation. Vascular bundles, which are scattered throughout the pith, are concentric amphicribal in Adelobotrys adscendens and Clidemia epiphytica (this one with a very reduced xylem), and just amphicribral in Blakeagranatensis. Blakea granatensis pith has fibers with a narrow lumen, thick walls, and simple pits; these fibers are found around the internal phloem and vascular bundles (Fig. 21).

Hemiepiphytes

Epidermis: The epidermis is absent in the fifth internode of Blakea rosea (Ruiz & Pav.) D. Don. In Blakea watsonii (Cogn.) Penneys & Almeda, the epidermis is single-layered and shows small cells. The developing periderm is located just below the epidermis, and trichomes one absent (Fig. 22A).

Periderm: The periderm is superficial, a single layer of continuous tissue. The phellem is one-layered in Blakea rosea, and two- to five-layered with scattered stone cells in Blakea watsonii. The phellogen is a one- to three-layered tissue of thin cells. The phelloderm cells have radial disposition; in Blakea watsonii it has one to two layers that accumulate druses; in Blakea rosea the number of layers varies from three to 15 layers, across the different regions of the transverse section (Figs. 22, 23).

Cortex: The cortex is mainly formed by parenchymatous cells with isodiametric shape, druses are accumulated only in Blakea rosea in a layer below the phelloderm. Only in these two species, a sclerotic parenchyma forms a two- to four-layered continuous tissue below the phelloderm (Figs. 22, 23).

Endodermis: In these two species, the pericycle was not observed. The limit between the cortex and the phloem is only taken up by the endodermis, having two- to six-layered tissues with cells smaller than cortical parenchyma and without cytoplasmic accumulations. Scattered fibers with thick walls, narrow lumen and simple pits are present (Figs. 22A, 23).

Phloem: Sieve-tube elements have a radial disposition in Blakea rosea, and are scattered in Blakea watsonii. Sieve plates are simple and transverse. Fibers in Blakea rosea form a one- to four-layered continuous tissue close to the endodermis, in Blakea watsonii the presence is rare. Axial parenchyma is present in a strand of short cells, some containing druses, more commonly close to the endodermis (Figs. 23A, 24).

Vascular cambium: The vascular cambium is a one- to three-layered continuous and uniform tissue of small cells that have walls with irregular shape (Fig. 24A, B).

Xylem vessels: The arrangement of vessels has a radial to diagonal pattern and the grouping is in multiples of two to three, or more commonly solitary. The outline of solitary vessels is angular. Perforation plates are simple and inclined. Intervessel pits are rounded, bordered and have an alternate arrangement (Figs. 25A-D).

Xylem fibers: The fibers are of the libriform type and have transversal septa. Blakea watsonii xylem shows just one type of dimorphic fibers, and Blakea rosea show two, in the same way that occurs in Blakea quadrangularis and Adelobotrys adscendens, respectively. The tangential bands of dimorphic fibers have two to three layers and the distance between bands is larger than the distance between rays (Figs. 25A-C, E).

Xylem axial parenchyma: The axial parenchyma is of the apotracheal type and formed by strands of short cells. In the xylem of Blakea watsonii, the axial parenchyma forms a tangential five-layered band of cells that contain druses and have irregular and wide lumens. In Blakea rosea the axial parenchyma cells are scarce, isolated, and containing prismatic crystals (Figs. 25A, E).

Xylem rays: The rays are uniserial, formed by upright and square cells. Vessel-ray pits are rounded to oval and half-bordered, with border only in the vessel lumen (Figs. 25E, F).

Pith: The pith periphery incorporates a continuous tissue of internal phloem. In the center, it is formed by parenchymatous cells that show isodiametric shape and accumulation of druses. Vascular bundles are concentric and amphicribral, with primary growth, and are scattered throughout the pith. Fibers show a narrow lumen, thick walls, and simple pits, and are located around the internal phloem and the vascular bundles (Fig. 26).

Epiphytes

This group only contains Monolena primuliflora Hook. f. The stem is composed by a wide periderm that gives it external support. Below the periderm, the stem is almost exclusively formed by parenchyma and a few narrow vessels from the adventitious roots. Therefore, for this species, it was not possible to delimit a cortex, vascular system, or pith in the inner area (Fig. 27A).

Periderm: The periderm is superficial and single-layered with lenticels. The phellem is five- to eight-layered with cells in radial disposition. Phellogen is one-layered with thin cells. The phelloderm is eight to 12-layered with cells containing druses, without radial disposition (Figs. 27B, C).

Parenchyma: Composed by large isodiametric cells that show little accumulation of material and lack intercellular spaces. In this inner tissue, there is neither growth direction, nor determined cellular arrangement (e.g. an endodermis). In the parenchyma, except for the xylem, no other cellular type or tissue is present (Figs. 27B-F).

Xylem: The xylem has primary growth and is formed by few narrow and short vessels. These vessels show helical thickenings that sometimes are reticulated, and reach from the adventitious roots base to the center of the stem and along the periphery below the periderm. The vessels split along their trajectory (Figs. 27C-F).

Summary of anatomical differences among growth habits

The stem anatomy characters that distinguished Melastomataceae growth habits are summarized here:

Quantitative differences among growth habits

Growth habits differed in the tangential diameter of solitary vessels (p<0.001; tree/shrub>herbs=vines; Fig. 28A), the number of vessels per mm² varied among growth habits (p<0.001; vines>hemiepiphyte=tree/shrub=herb>liana; Fig. 28B) and the vessel axial length (p<0.001; hemiepiphyte>three/shrub=liana=vine>herb; Fig. 28C). Species was a significant factor in the three ANOVAs (p<0.001).