Abrus Adans.

Scientific Description

Family Papilionaceae. Abreae.

Habit and leaf form. Ours lianas; ours deciduous. Leaves well developed. Plants unarmed. Plants with neither basal nor terminal concentrations of leaves. Climbing; stem twiners. Twining clockwise, or twining anticlockwise. Mesophytic, or xerophytic. Leaves medium-sized; not fasciculate; alternate; spiral, or distichous; ‘herbaceous’, or leathery; not imbricate; petiolate; non-sheathing; compound; pulvinate; pinnate; paripinnate (terminating in a bristle, cf. Vicieae). Leaflets 10–40 (? — ‘numerous’). Lateral leaflets opposite. Leaflets minutely stipellate; pulvinate, or epulvinate; flat; without lateral lobes. Leaf blades dorsiventral; cross-venulate. Leaves with stipules. Stipules intrapetiolar; adnate to the petiole, or free of the petiole; free of one another; setaceous; caducous, or persistent. Leaves without a persistent basal meristem. Stem anatomy. Nodes tri-lacunar, or penta-lacunar. Secondary thickening developing from a conventional cambial ring, or anomalous; if anomalous, via concentric cambia.

Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Anemophilous, or entomophilous.

Inflorescence and flower features. Flowers aggregated in ‘inflorescences’; not crowded at the stem bases; in racemes and in fascicles. Inflorescences compound. The terminal inflorescence unit cymose, or racemose. Inflorescences terminal, or axillary; in pseudoracemes of axillary fascicles, the pseudoracemes terminal or axillary, the fascicles sometimes secund. Flowers pedicellate, or subsessile; bracteate (the bracts small); bracteolate (the bracteoles small); small to medium-sized; very irregular; zygomorphic; resupinate, or not resupinate. The floral asymmetry involving the perianth and involving the androecium. Flowers papilionaceous (imbricate-descending, with the posterior petal outside and forming a the ‘standard’); basically 5 merous. Floral receptacle developing a gynophore to with neither androphore nor gynophore (the ovary subsessile). Free hypanthium present, or absent. Perianth with distinct calyx and corolla; 10; 2 -whorled; isomerous. Calyx present; 5; 1 -whorled; gamosepalous; lobed (denticulate). Calyx lobes markedly shorter than the tube (the calyx truncate, the teeth very short). Calyx imbricate, or valvate; exceeded by the corolla; campanulate; somewhat bilabiate (the posterior pair of lobes joined higher); non-fleshy; persistent; non-accrescent; with the median member anterior. Epicalyx absent. Corolla present; 5; 1 -whorled; appendiculate (the standard with small, inflexed auricles), or not appendiculate. Standard appendaged. Corolla partially gamopetalous. 2 of the petals joined, or 4 of the petals joined (the two ventral petals abaxially adnate to form the ‘keel’, and ‘interlocked with the wings’). The joined petals of the papilionate corolla anterior (and lateral). The wings of the corolla adherent to the keel; not laterally spurred. Standard ‘normally’ developed (the limb ovate); emarginate; not sericeous (glabrous). Keel conspicuously exceeding the wings (longer and broader, shallowly falcate); not long-acuminate/beaked; neither coiled nor spiralled; not bent and beaked. Corolla imbricate (descending); in ours, pink, or purple to blue (or mauve); non-accrescent. Petals clawed. Androecial members definite in number. Androecium 9 (the vexillary member missing). Androecial sequence determinable, or not determinable. Androecial members adnate (according to Bentham, ‘the broad claw of the standard adnate to the androecial tube’, but other accounts merely state that the standard is ‘sessile’); all equal to markedly unequal (sometimes alternately long and short); coherent (the filaments connate into an adaxially split sheath); 1 - adelphous. The staminal tube adnate to the keel petals, or free from the keel petals. Androecial members 1 -whorled (although diplostemonous). Androecium exclusively of fertile stamens. Stamens 9 (the vexillary stamen missing); all more or less similar in shape; (sub-) diplostemonous; both opposite and alternating with the corolla members. Anthers separate from one another, or connivent; dimorphic to all alike (sometimes 4 of them somewhat smaller); dorsifixed; versatile; dehiscing via pores, or dehiscing via longitudinal slits; latrorse, or introrse; tetrasporangiate. Gynoecium 1 carpelled. The pistil 1 celled. Carpels reduced in number relative to the perianth. Gynoecium monomerous; of one carpel; superior. Carpel stylate; apically stigmatic. Style (in-) curved (short). Style glabrous. Stigmatic tissue terminal. Carpel 4–20 ovuled (‘several’ or ‘many’). Placentation marginal (along the ventral suture). Gynoecium median (the placenta posterior, on the ventral suture). Ovary sessile to subsessile. Ovary summit hairy, the hairs not confined to radiating bands. Stigmas capitate. Ovules pendulous to ascending; biseriate; arillate; anatropous, or campylotropous to amphitropous, or hemianatropous.

Fruit and seed features. Fruit sessile; non-fleshy; appressed hairy. The fruiting carpel dehiscent; a legume. Pods somewhat elongated to much elongated (oblong to linear); not triangular; straight; not becoming inflated; more or less flat to somewhat compressed; regularly constricted between adjacent seeds; more or less transversely septate between the seeds; wingless. Valves of the dehisced pod twisted. Fruit 1 celled (usually), or 2 celled (rarely, by longitudinal intrusion of the placenta); elastically dehiscent, or passively dehiscent. Dispersal unit the seed. Fruit 3–7 seeded (in ours). Seeds endospermic, or non-endospermic; not mucous; (sub-) compressed, or not compressed; small to medium sized; arillate. Cotyledons 2; accumbent. Embryo chlorophyllous; curved to bent (the radicle incurved). Testa non-operculate; homogeneous in colour, or conspicuously colour-patterned. Micropyle zigzag, or not zigzag. Seedling. Germination phanerocotylar.

Physiology, biochemistry. Nitrogen-fixing root nodules present. Aluminium accumulation not found. Photosynthetic pathway: C₃.

Geography, cytology, number of species. Native of Australia. Not endemic to Australia. Australian states and territories: Western Australia, Northern Territory, Queensland, and New South Wales. Northern Botanical Province. 2n=20, 22, 24. A genus of 17 species; 1 species in Western Australia.