Dicorynia Benth.

Falcão, Marcus José De Azevedo, Torke, Benjamin Marland & Mansano, Vidal De Freitas, 2022, A Taxonomic Revision of the Amazonian Genus Dicorynia (Fabaceae: Dialioideae), Phytotaxa 554 (1), pp. 1-31 : 4-11

Dicorynia Benth. in Hook., J. Bot. 2: 82–83 (1840).

Type: — Dicorynia paraensis Benth.

Spelling variant: Dicorynea Lindl. The Vegetable Kingdom: or, the Structure, Classification, and Uses of Plants, Illustrated Upon the Natural System: 555 (1847).

Trees, (6–) 8–45 (–50) m tall; trunk with or without buttresses up to 2 m tall, heartwood red, brown, or gray, sapwood generally lighter, but not always easily distinguishable from heartwood; exudate present and gelatinous or absent; bark cracked, rough, or peeling, gray to brown, sometimes with red stripes, with or without lenticels; branches unarmed. Leaves, imparipinnate, alternate, pulvinate; leaflets (3–) 5–11 (–13), elliptical, ovate, or oblong, alternate, subopposite, or opposite, discolorous, glabrous to slightly pubescent abaxially, glabrous adaxially, with surface papillate or not, apex generally acuminate to caudate, more rarely acute, base cuneate, obtuse, cordate, or truncate, margin entire, revolute or not, venation brochidodromous; axillary buds laterally oblong, elliptical, obovate, orbicular or lanceolate, being acuminate, acute, or obtuse at apex, frontally triangular or orbicular, brown, gray, or black; terminal buds strongly capitate with the apex generally orbicular or more rarely rounded or acuminate, brown gray, or black, enveloped by two reniform to ovate, pubescent, deciduous stipules. Inflorescences thyrsoid, distichous, compound, with 1–3 levels of subthyrsoids, terminal, rarely axillary, up to 50 cm long, the axes sericeous to pilose, rarely tomentose, golden to brown to dark brown; two bracts subtending triads of flowers or inflorescence axes, caducous, oblong to elliptical, apex obtuse to acuminate; bracteoles absent. Flower buds globose to elliptical; flowers asymmetric due to the heteromorphic stamens; receptacle flat, with a short, curved and narrow cavity between the carpel and the abaxial sepal, forming a shallow hypanthium, strongly pilose; calyx zygomorphic, composed of five heteromorphic sepals of two types: 1) three outermost sepals (very rarely four), free, two lateral and one abaxial, strongly imbricate, with the outermost sepal or two outermost sepals covering almost the entire floral bud, these three sepals concave, externally brown, reddish, or whitish, internally white with reddish or brown base, densely sericeous abaxially, rarely pilose or tomentose, brown, golden, or white, glabrescent adaxially, base truncate, apex rounded, margin entire, caducous but persisting longer than the inner sepals and petals; 2) two innermost sepals (very rarely one or none) petaloid, free, abaxially lateral, slightly imbricate, white, slightly to densely sericeous abaxially, brown, golden, or white, glabrescent adaxially, slightly clawed, base cuneate, apex rounded, margin entire, caducous but persisting longer than the petals; corolla zygomorphic comprising three (very rarely two or four) free petals, two lateral and one adaxial, with strongly imbricate aestivation, the adaxial petal external to the others, all three petals white or more rarely slightly pink, with or without brown or reddish spots, sparsely to densely sericeous abaxially, glabrescent adaxially except by the base with white, golden, or brown trichomes, strongly unguiculate, obtuse to reniform at base, obtuse, rounded, or truncate at apex, the margin wavy or entire, caducous; androecium asymmetric with two (very rarely 1–3) stamens, the stamens adaxial, alternating with the petals, dimorphic, with the longer filament supporting the narrower anther and the shorter filament supporting the wider anther, the position of the longer and shorter stamen in the flower alternating in a mirrored way based on the position of the flower in the cyme; filaments of both stamens as wide as the anthers, glabrous, white or slightly rosy-reddish, sometimes with brown or reddish spots, strongly ventrally furrowed, the connective with a large and truncate apex presenting uncinate trichomes, anthers basifixed, introrse, yellow to cream, sometimes with brown or reddish spots, oblong, poricidal, with two apical pores partially covered by the anther tip, thecae almost glabrous except for the apex which sometimes bears uncinate trichomes, anther of the longer stamen curved and narrower than that of the shorter stamen, with the apex facing the stigma, 4-sporangiate or (6–) 8-sporangiate, with four sporangia at the base and others proliferating distally, anther of the shorter stamen straight and wider, 8–11-sporangiate, with four sporangia at the base and others proliferating distally, the extra sporangia in both anthers being visible externally by the formation of protuberances on the anther surface, pollen spherical, tricolpate, colpae elongated, ornamentation of the exine punctate; ovary laterally compressed, sessile to slightly stipitate, displaced to abaxial periphery of the flower, straight or with winding shape, densely sericeous, black or brown, bearing 2–6 ovules, glabrous or pubescent on the inner wall of the locules, style curved towards the adaxial face of flower, glabrous, white, with the suture of the carpel cleft visible at anthesis, stigma punctate, papillate, Fruits samaroid, coriaceous, lignified, strongly laterally compressed, green when immature, light to dark brown to slightly purple when mature, very rarely blackened, glabrous or with a microscopic and sparse indumentum, circular to oblong, both margins curved to wavy, sometimes asymmetrical to each other, sometimes the small style persistent, terminal, discretely parallel veined, very rarely fissured, supplied with a narrow wing along the entire adaxial suture, base obtuse, truncate, or asymmetric, essentially indehiscent, very rarely tardily opening by the adaxial suture when deteriorated. Seeds 1–3 (–5), not arillate, light or dark brown, circular, quadrilateral, or slightly reniform, testa weakly striate, endosperm white, with a transparent and gelatinous marginal region, surface of the endosperm with circular perforations at the microscopic level; cotyledons light green, caducous after germination; hypocotyl-radicular axis straight, positioned in the abaxial-central region of the cotyledons; plumule and leaf primordia well-developed. Seedlings with the first pair of eophiles opposite, others alternate, the first 4–5 eophiles unifoliolate, generally ovate, and cordate or truncate at base, succeeding eophiles trifoliolate.

Diagnosis: — Dicorynia differs from the other genera of Fabaceae by the following combination of characters: imparipinnate leaves; thyrsoid inflorescences with distichous branching; three outer sepals, two inner petaloid sepals, and three petals; two dimorphic stamens with strongly furrowed filaments; basifixed and poricidal anthers of width similar to that of the filaments, one or both polysporangiate; and samaroid fruits with a narrow wing along the adaxial suture.

Distribution, Habitat, Biogeographical Patterns, and Ecology: — Dicorynia is endemic to the Amazonian region of South America , where it has been recorded from French Guiana, Guyana, Suriname, Colombia, Peru, Venezuela, and the Brazilian states of Amazonas, Pará and Amapá. The genus occurs in a variety of humid tropical forest types, both well-drained and seasonally inundated, including “igapó”, “várzea”, “campinarana”, and “terra firme”, and is frequently associated with rivers.

The distribution of polysporangy among the two anthers of the flower displays complete correlation with a geographical disjunction between populations in the Guianas ( D. guianensis ) and the Amazon basin ( D paraensis ), corroborating the hypothesis by Koeppen (1967).Several other characters display partial correlation with the disjunction. While the area intervening in the geographical ranges of the two species is poorly collected, it is reasonable to assume that the disjunction is real. Both species are known only from low elevation (less than 600 meters in D. guianensis and 200 meters in D. paraensis ), high humidity areas (2000–3700 mm average annual precipitation), a pattern similar to that observed in the Neotropical genus of Dialioideae Androcalymma , but strongly contrasting to other taxa in Dialioideae , such as Poeppigia , Apuleia , and several species of Martiodendron and Dialium that usually occur in less humid forests, including the Cerrado and Caatinga (Fig. 10) ( Falcão et al. 2020b, 2021, unpubl. data). Thus, the high elevation regions of the Guiana plateau in the southern Guianas and northern Brazil and the associated low-precipitation belt in the north Pará, Roraima, and Guianas may function as an effective geographic barrier, preventing gene flow between the two species (Figs. 5, 10). Presumably, the strength of this barrier would have been even more pronounced during glacial maxima, when the climate of the region was markedly drier ( Prance 1973, Bush and Oliveira 2006, Haffer 2008). The distribution pattern suggests a recent process of allopatric speciation, corroborated by the remarkable morphological similarity between the two species.

Etymology: —The genus was named by Bentham from the Greek, “ di ” (two) and “ corynia ” (club), referring to the characteristic two club-shaped anthers.

Taxonomic Comments: —Despite the phenotypic plasticity of leaves in the genus, patterns distinguishing the infra-generic taxa could be observed. In D. paraensis , both var. ingens and var. macrophylla have generally 11 leaflets and never less than nine. The leaflets are commonly seven and five in var. uaupensis and var. paraensis , very rarely exceeding nine. In D. guianensis , seven leaflets are found in almost all individuals. Although the size of the leaflet is variable in all taxa, the shape is stable in D. guianensis , being almost always oblong, relatively stable in D. paraensis, var. ingens and var. macrophylla . It is generally broadly ovate in the first and narrowly oblong in the second, and more variable in var. uaupensis and var. paraensis . The narrowly elliptical shape is more common in the first, and the broadly ovate in the second. Sometimes, morphologically variable specimens of var. paraensis and var. uaupensis can resemble each other in this character, making it difficult to distinguish them by it. The petiolule size is a strong character, being longer in var. paraensis and var. macrophylla and shorter in var. uaupensis and var. ingens (Figs. 2A–C; 4D–E, H; 7).

According to Koeppen (1967), papillae in the epidermis of the leaflet’s abaxial face would be present in varieties breviflora , floribunda , and ingens and in D. guianensis . Varieties macrophylla , paraensis , and uaupensis would not have such papillae. The leaflets’ surface present papillate ornamentation in several specimens under high-resolution stereomicroscope. D. guianensis is very stable with the majority of its specimens’ leaflets presenting papillae, but no significant distribution pattern for this character could be traced among D. paraensis populations, with the majority of specimens in varieties macrophylla and paraensis having non-papillate leaflets but with several exceptions. With the broader circumscription proposed here for var. uaupensis , including the synonymized varieties breviflora and floribunda , we have groups of specimens with leaflets varying from strongly papillate to non-papillate. Such groups could not be separated from each other with any other character. They also present a completely overlapping distribution.

Koeppen (1967) and Gunn (1991) considered the fruits of Dicorynia (Figs. 2I; 4M–N) as tardily dehiscent follicles, while Bentham (1870), Record and Hess (1943), Milanez and Mattos Filho (1959), Rizzini (1971), and Jesel (2005) considered them indehiscent. Here, no open mature fruit was seen in many living individuals and herbarium specimens. Very rarely, in dispersed fruits in an advanced state of decomposition, the deterioration of one of the sutures allowed the visualization of the seeds. This, added to rare specimens with fruits with detached wings (with the seed chamber still sealed), may have led to the tardily dehiscent interpretation. Thus, we maintain here the concept of indehiscent fruits for Dicorynia . Barroso et al. (1999) identified the fruit of the genus, sometimes as samaras (pgs. 179; 188) or as nucoid legumes (pg. 189). The authors separate samaras from samaroid legumes indicating that the first group has wings and a monospermic seminal nucleus distinct from the wing. The second has few to many seeds per seminal nucleus, that is a little distinct or indistinct from the wing. They define nucoid legumes as indehiscent or late dehiscent fruits with dry pericarp, which is distinguished from the nucules by having few to many seeds. Nucules, different from nucoid legumes, would have adaptations for anemochory or hydrochory due changes in calyx or other floral involucres. In Dicorynia , such adaptations are due to the vestigial wing, the lateral compression of the fruit, and the appearance of a narrow cavity with air in the seed chamber. All of these modifications are also found in its closely related genus Apuleia . On the other hand, the definition as nucoid legumes based on dispersion form does not seem prudent in Dicorynia , since morphologically identical fruits can be hydrochorically dispersed in D. paraensis var. paraensis , for example, and anemochorically in D. guianensis (see comments on both taxa). Thus, added to the presence of a few seeds in the fruit and the underdeveloped wing, we consider the fruits of Dicorynia as samaroid legumes, as in other Dialioideae genera ( Falcão et al. 2021, unpubl. data). The fruits of Dicorynia vary from elliptical to oblong and many intermediate forms are found in all taxa, as already pointed out by Koeppen (1967). However, larger oblong fruits are much more common in D. paraensis var. macrophylla and D. guianensis and considerably rare in the other taxa. The color, texture of wing more or less rigid, the width of the wing, the venation pattern, and the veins impression are variable among individuals. However, two Venezuelan specimens of var. uaupensis (P.E. Berry 7460; M. Yanez 481) have thicker, blackish, heavily fissured, circular, and symmetrical fruits, differentiated from other specimens. Considering that they are vegetatively identical to other Venezuelan specimens with common fruits (K.M. Redden 3730), the mentioned distinctions seem to be just a rare variation.

Seedlings of Dicorynia (Figs. 9A–D) resemble those of closely related genera such as Dialium , Apuleia , and Martiodendron Gleason ( Hartmann and Rodrigues 2014, Falcão et al. unpubl. data). Dicorynia has well-developed leaf primordia in the seed (Figs. 9M–N) and the first 4–5 eophiles wide and unifoliolate, with a truncate to cordate base, followed by trifoliolate eophiles and, subsequently, by imparipinnate leaves with alternating leaflets (Figs. 9A–D). The genus Poeppigia C. Presl , ( Falcão et al. 2021), early diverging in Dialioideae phylogeny, differs from the other mentioned genera in that it has inconspicuous leaf primordia, only the first pair of unifoliolate eophiles, narrow, and with a cuneate base, and the following eophiles with several leaflets and paripinnate. The endosperm of Dicorynia resembled that of Martiodendron (Falcão et al. unpubl. data), with the first having a partially gelatinous endosperm on its margin and the second having a completely gelatinous endosperm. Dialium , Apuleia , and Poeppigia have completely solid endosperm ( Falcão et al. 2021, unpubl. data). The morphology of the seedlings is very similar between D. paraensis (Figs. 9A–D) and D. guianensis ( Jesel 2005) , as also the morphology of seeds (Figs. 9E–I, L), embryos (Figs. 9J–K, M–N), and pollen (Fig. 9R). The morphology of the anther is variable among the two species of the genus (Figs O–Q). Among the four varieties of D. paraensis such structures are also very stable, with no considerable variation.

Identification key to species in Dicorynia

1. Anthers of both stamens polysporangiate, those of the longer stamen with (6–) 8 sporangia in the median to apical region; ovules usually 4–6; leaflets (3–) 7 (–11), almost always oblong; occurring in Suriname, Guyana, and French Guiana; usually in nonflooded forests ................................................................................................................................................... Dicorynia guianensis

1. Only the anthers of the shorter stamen polysporangiate, those of the longer stamen with 4 sporangia along its entire length; ovules usually 2–4; leaflets 5–11 (–13), elliptical, ovate, or oblong; occurring in the Amazon basin, in the Brazilian states of Amazonas, Pará, Amapá, and adjacent areas of Venezuela, Colombia and Peru; in flooded forests or on dry land ............. Dicorynia paraensis