Flora of the Hawaiian Islands
Dicotyledon Literature for Senna occidentalis
Lorence & Wagner, 2020.
   Fabaceae -- The Pea Family Bibliography
      Senna occidentalis

Common name(s): `au`auko`i, `auko`i, coffee senna, mikipalaoa, pi hohono
General Information
DistributionWidespread in tropical Africa, India, Sri Lanka, SE Asia, Malesia, Australia, and many Pacific islands, also in North and South America, possibly native to the Old World.In the Hawaiian Islands, naturalized on Ni`ihau, Kaua`i, O`ahu, Moloka`i, Maui, Hawai`i.

Foetid annual or perennial herb or subshrub, 0.4‒2 m tall, sometimes somewhat woody toward base.
Leaves petiolate; leaflets (3)4‒5(6) pairs, distal ones larger, broadly lanceolate to ovate, 4.5‒10 cm long, 1.4‒3.8 cm wide, adaxial surface glabrous, abaxial surface glabrous to sparsely coarsely puberulent, margin antrorsely ciliate, apex acuminate, base obliquely rounded; petiole 3.5–5 cm long, single sessile nectary contiguous to the pulvinus, 0.7‒1.8 mm long, sometimes a second one adjacent; stipules deltate to lanceolate, 3‒13 mm long, caducous.
Inflorescences terminal or axillary racemes of up to ca. 10 flowers, pedicel 8‒17(‒21) mm long; bracts lanceolate to oblanceolate, 5‒18 mm long. Flowers with calyx lobes pale or pinkish tinged, submembranous, obovate or oblong-obovate, outer one 5‒7.5 mm long, longest inner one 6.5‒10 mm long; petals yellow, subequal, standard usually obcordate, 2 lateral petals obovate, others oblanceolate, 12‒17 mm long; staminodes 3, 0.7‒1.2 mm wide, filaments of 4 median stamens 2‒3.3 mm long, those of 2 abaxial stamens dilated, 5‒7 mm long, that of sterile abaxial central stamen 3‒4 mm long.
Fruit erect or ascending, coriaceous, linear, compressed, slightly curved or straight, 8‒13.5 cm long, 6.5‒9.5 mm wide, margin of valves green when young becoming straw colored, body reddish green becoming brown, dehiscent, cavity with membranous interseminal septa.
Seeds dull olive to grayish brown, compressed obovoid to compressed suborbicular, 4‒5 mm long, 3‒3.5 mm wide, nearly smooth, waxy exterior coat crackled with age, areole ca. 2.5 mm long, 1.5 mm wide.
2n = 26, 28.
Nancy Khan