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The genera of Leguminosae-Caesalpinioideae & Swartzieae

L. Watson and M.J. Dallwitz

Intsia Thouars

Macrolobium Zipp. ex Miq. (not Schreb.)

Type species: I. bujuga (Colebr.) O. Ktze. (I. madagascariensis Thouars).

Habit and leaf form. Trees; unarmed.

Phyllotaxy distichous, or spiral. The leaves compound; pinnate, or bifoliolate; paripinnate. The leaflets few per leaf; opposite or sub-opposite (their undersides usually with one or two small, crateriform glands at the base); petiolulate; with markedly twisted petiolules, or without noticeably twisted petiolules; markedly asymmetrical to symmetrical or nearly so; pinnately veined, with a predominant ‘midrib’ (this tending to be displaced upwards); without a continuous marginal nerve. Stipules present, persistent and conspicuous in mature leaves; connate (forming a persistent intrapetiolar scale). Stipels absent.

Inflorescence and floral morphology. The inflorescences terminal; unbranched and branched; when branched, of racemose units; simple racemes and panicles. The flowers not distichous. Bracts absent at anthesis. Bracteoles present; small, not enclosing the flower buds; absent at anthesis; not valvate; free.

The flowers hermaphrodite; not pentamerous throughout; departing from pentamery in the calyx and in the corolla, 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. The perianth comprising distinct calyx and corolla. Calyx 4; covering the rest of the flower in bud; polysepalous; more or less regular to markedly irregular; members imbricate. Corolla present; very irregular; 1, or 2–5 (comprising one large orbicular or reniform adaxial petal, with or without vestiges of others); including greatly reduced members, or without greatly reduced members; polypetalous. Petals clawed (the large one), or sessile; when not monopetalous, imbricate; white, or red. Disk absent. The androecium comprising 7–10 members; declinate; with united members (the long filaments basally connate); members markedly unequal; including staminodia. The staminodia 4–7. Fertile stamens 3 (these lateral and abaxial). Anthers attached well above the base of the connective; dehiscing introrsely; dehiscing longitudinally. Ovary stipitate; eccentric, with the stipe adnate. Stigma dilated (capitate on the long, slender style). Ovules few to numerous (several, uniseriate).

Fruit, seed and seedling. Fruit a two-valved pod; without markedly twisting or enrolling valves; compressed, flat and thin, not becoming woody. The mature valves with conspicuous, prominent, raised venation to without prominent venation; conspicuous venation transverse, not predominantly longitudinal. Seeds not arillate; with a straight or slightly oblique radicle; amyloid-positive. Cotyledons of Type 4; with a vascular system in one plane.

Transverse section of lamina. Leaves with conspicuous phloem transfer cells in the minor veins. Druses common in the mesophyll. Mesophyll secretory cavities absent. Adaxial hypodermis absent. Leaf girders absent. Laminae dorsiventral. Mesophyll without unaligned fibres or sclereids. Minor veins mainly with abundant accompanying fibres.

Leaf lamina epidermes. Epidermal crystals not seen either adaxially or abaxially. Simple unbranched hairs common; 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 absent. Adaxial: Adaxial interveinal epidermal cell walls markedly sinuous in high-focus optical section; not conspicuously pitted; medium-thick. 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; thick.

Wood anatomy. Intervascular pits very small.

Pollen ultrastructure. Tectum reticulate; strongly irregularly coarse-reticulate. Length of colpi less than one half pole to pole distance. Foot layer of pollen wall with obvious projections.

Cytology. Basic chromosome number, x = 12. 2n = 24.

Species number and distribution. 2 species (I. bijuga and I. palembanica; excluding some species referred to Afzelia). Tropical East Africa, Madagascar, tropical Asia, Malaysia.

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

Miscellaneous. Illustrations: • I. palembanica: Ding Hou, Fl. Malesiana 12 (1995). • I. bijuga, 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: 22nd March 2017.’.