| # The genera of Leguminosae-Caesalpinioideae and Swartzieae |

L. Watson and M.J. Dallwitz

### Heterostemon Desf.

Heterostemum Steud.

Type species: H. mimosoides Desf.

Habit and leaf form. Trees, or shrubs; unarmed.

Phyllotaxy spiral. The leaves compound, or ostensibly simple; when unifoliolate, pinnately veined with a predominant midrib; when compound, pinnate (but the lateral leaflets sometimes very reduced); imparipinnate, or paripinnate. The leaflets many per leaf, or few per leaf (few to many jugate); opposite or sub-opposite, or alternate; sessile to sub-sessile; without noticeably twisted petiolules; markedly asymmetrical to symmetrical or nearly so (?); with a predominant ‘midrib’; without a continuous marginal nerve. Stipules present, persistent and conspicuous in mature leaves, or absent or early caducous or very inconspicuous in mature leaves; leafy, or membranous. Stipels absent.

Inflorescence and floral morphology. The inflorescences at the tips of shoots or at defoliated nodes; unbranched; short, sessile simple racemes. The flowers not distichous. Bracts caducous, small, absent at anthesis. Bracteoles present; small, not enclosing the flower buds (at the tip of the pedicel, very much shorter than hypanthium); persistent beyond anthesis; not valvate; tiny, connate.

The flowers showy; hermaphrodite; not pentamerous throughout; departing from pentamery in the calyx and in the androecium, or in the calyx, in the corolla, and in the androecium; coloured. Floral tube length relative to total hypanthium + calyx length about 0.5. Hypanthium present; asymmetrically long tubular. Calyx petaloid, 4; covering the rest of the flower in bud; more or less regular; members imbricate. Corolla present; very irregular (having the three petals, or the three well developed ones, similar to one another); 3, or 5; including greatly reduced members (the lower two), or without greatly reduced members (then with the lower two absent); polypetalous. Petals imbricate; imbricate-ascending; red. Disk absent. The androecium comprising 9 members; with united members (connate into an adaxially split sheath); members markedly unequal (having three of the abaxial members longer than the other six); including staminodia. The staminodia 6; shorter than and alternating with or adaxial to the perfect stamens, the anthers lacking or imperfect. Fertile stamens 3 (the 3 long members with perfect, oblong anthers). Anthers attached well above the base of the connective; dehiscing longitudinally. Ovary stipitate; eccentric, with the stipe adnate (the style filiform). Stigma small, but dilated (capitate on the long, slender style). Ovules few, or numerous.

Fruit, seed and seedling. Fruit a two-valved pod; compressed, straight, or curved (straight or falcate); leathery, not becoming woody. The mature valves without prominent venation. Seeds non-endospermic; not arillate; with a straight or slightly oblique radicle.

Transverse section of lamina. Leaves with conspicuous phloem transfer cells in the minor veins. Druses absent from the mesophyll. Mesophyll secretory cavities absent. Adaxial hypodermis absent. Leaf girders absent. Laminae dorsiventral. Mesophyll exhibiting fibres or sclereids which are unaligned with the vascular bundles. Minor veins mainly with abundant accompanying fibres.

Leaf lamina epidermes. Epidermal crystals not seen either adaxially or abaxially. Simple unbranched hairs common; scabrid, or smooth. No compound or branched eglandular hairs seen. Capitate glands not seen. Hooked hairs not seen. Cassieae-type leaf pseudo-glands not seen. Expanded and embedded hair-feet present; (at least some of them) thin-walled; hair feet (at least some of them) complex with vertical walls. Adaxial: Adaxial interveinal epidermal cell walls markedly sinuous in high-focus optical section; not conspicuously pitted. Stomata adaxially very rare. Abaxial: Abaxial stomata predominantly paracytic. Abaxial epidermis not papillate. Abaxial interveinal epidermal cell walls markedly sinuous in high-focus optical section; conspicuously pitted in optical section; staining normally with safranin.

Wood anatomy. Wood not storied.

Pollen ultrastructure. Tectum striate; pole to pole striate. Length of colpi greater than one half pole to pole distance.

Species number and distribution. 7 species. Tropical America.

Tribe. Detarieae; Amherstieae clade of Bruneau et al. (2008).

Miscellaneous. Illustrations: • Heterostemon ellipticus and H. mimosoides: Fl. Brasiliensis 15 (1870). • Heterostemon confugatus, e.m. scanned pollen (Graham & Barker, 1981).

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, and classification. See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1993 onwards. The genera of Leguminosae-Caesalpinioideae and Swartzieae: descriptions, illustrations, identification, and information retrieval. In English and French. Version: 4th August 2019. delta-intkey.com’.

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