VIII. LEUCOCHLORON Barneby & Grimes
Leucochloron Barneby & Grimes, gen. nov., hinc Chloroleuco, illinc Blanchetiodendro affine et utroque gemmis perulatis simile, sed a priori spinis axillaribus (pedunculis sterilibus induratis) nullis, legumine lato-lineari plano-conpresso necnon seminum disciformium testa membranacea exareolata, a Blanchetiodendro, quoad legumen et semina congruo, capitulis axillaribus (nec pseudoracemosis paniculatisve) flosculisque capitatis homomorphis (nec umbellatis heteromorphis) distans. — Sp. typ- ica: L. incuriale (Vellozo) Barneby & Grimes = Mimosa incurialis Vellozo. — Etymology: Gr. leu- cos, white + chloros, greenish yellow; anagram of Chloroleucon.
Unarmed, multi- or plurifoliolate trees with monopodial branches, the young growth puberulent or pilosulous with pallid, yellowish or rusty hairs; a perulate bud of often striate scales in the axil of many mature lvs and at apex of branchlets. Stipules caducous. Lf-formula (i—)ii—ix/4—27; petiolar nectaries sessile, cupular or almost plane, the first one borne usually between or close below proximal pinna-pair, but sometimes below midpetiole; lft-pulvinules mostly <1 mm; venation of lfts palmate-pinnate, or in L. foederale primarily pinnate. Flowers capitulate homomorphic, the capitula either solitary or fasciculate, borne on homotinous branchlets either immediately below or axillary to coeval lvs; perianth 5- merous, the calyx deeply campanulate, the corolla tubular-infundibuliform; androecium 20-40-merous, the tube about as long as corolla or often well exserted, the filaments white; no intrastaminal disc; ovary sessile or almost so, in profile elliptic; stigma scarcely or not dilated. Pods (unknown in L. minarum) sessile or shortly stipitate, in profile broad-linear, either straight or gently decurved, the valves stiffly papery or coriaceous; dehiscence tardy, inert, through one or both sutures, the valves narrowly gaping to emit the seeds; funicle filiform; seeds transverse, discoid (<1 mm thick), either discrete in one rank or imbricate, the thin, lustrous and translucent testa narrowly winged peripherally and girdled with a submarginal nerve, lacking pleurogram; endosperm 0.— Spp. 4, of Atlantic and planatine Brazil, from NE Bahia S to Paraná, inland to montane Minas Gerais, and to Distrito Federal; a partially known mimosoid tree found in the middle Orinoco Valley in state of Guárico, Venezuela, is suggestive of a fifth, distantly disjunct species of the genus.
The generitype of Leucochloron was misplaced by Bentham (1875: 591) in Pithecolobium ser. Coriacea (= Macrosamanea of this revision), from which it differs in perulate resting-buds, in inflorescence architecture, in lack of nectary on lower bracts of the capitulum, and in thin shiny disciform seeds. Nielsen (1981: 190) treated it as of unknown affinity, characterized by floral traits of Albizia but by seeds reminiscent of Zygia. We have not confirmed the presence of a hexamerous terminal flower with two ovaries, described by Nielsen, and suppose he must have happened on a random anomalous flower such as occurs rather frequently in pithecellobioid Ingeae. Leucochloron incuriale forms an apparently natural group with L. minarum and L. foederale, which collectively resemble Chloroleucon in striate perules and in inflorescence-type, but differ in the lack of thorny axillary branchlets, in the broad, stiffly papery pod, and in the discoid exareolate seeds. Its inflorescence is essentially that of Enterolobium, which differs most obviously in the obese indehiscent fruit.
A potential addition to the four species described below is the couvi, mentioned by Lewis (1987: 180) as related to L. incuriale but differing in the pod, which is contricted between seeds as in Pseudopiptadenia. This puzzle is known from the São Francisco valley near Barreiras in western Bahia; we have seen no specimens. A fragmentary branchlet bearing two leaves and immature pods, collected in the state of Guárico, Venezuela (Río Tamanaco, H. M. Curran 703, NY), has the perules of Leucochloron and a broad, piano-compressed fruit compatible with this genus (seeds not seen). We cannot assimilate this specimen into any mimosoid described or recorded from Venezuela and hazard the guess that it may represent another instance of amphi-Amazonian disjunction.
As the species of Leucochloron differ primarily in number of pinna-pairs or leaflets, or by autapomor- phic characters, their relationships are not resolved (Fig. 10). Furthermore, the fruit of L. minarum is still unknown.