Senna williamsii (Britton & Rose) H. S. Irwin & Barneby

Peiranisia williamsii Britton & Rose, sp. nov
A shrub about 3 m. high, the young branches long-pilose and densely puberulent, the long hairs sometimes deciduous. Leaves narrow, 10-15 cm. long; stipules 6-8 mm. long, narrow, acuminate, caducous; leaflets 40-60 pairs, linear, 8-12 mm. long, obtuse, glabrous, a slender clavate gland between the lower pair or pairs of leaflets and narrow linear glands between the upper pairs, sometimes between all of them; inflorescence axillary, few-flowered, sometimes, apparently, reduced to a single flower; peduncles 1.5-3 cm. long; pedicels 1.5-2.5 cm. long; flowers 3.5-4 cm. broad; petals yellow; three of the longer anthers stout-beaked; legume narrowly linear, 12-14 cm. long, 4 mm. wide, glabrate, stipitate, short-tipped, impressed between the seeds.
Costa Rica and Panama. Type from Bistnark, above Penonome, Panama, March 18, 1908, R. S. Williams 567.