The petals may be white, pink, purple or blue, often with a differently colored nectar guide, that may sometimes even be yellow.

Left and right of the base of the leafstalk, are two softly hairy stipules that may be partly merged with the stalk or entirely free, and are oval with a pointy tip or awl-shaped, while several veins create a striped appearance.

[2] The flowers are seated or on a very short stalk, growing in inflorescences consisting of 1 or 5-18 groups of 3 or rarely 2, set in the leaf axils or at the tip of the stems.

From it develops a swollen, softly hairy fruit that ends in a slight beak and protrudes from the calyx when ripe.

[2] Otholobium differs from Psoralea and Hallio by the lack of a cupulum, a small, 2- or 3-lobed bract that encircles the peduncle between its base and the calyx.

This was followed in 1794 by Jean Louis Marie Poiret who added P. acuminata, P. ononoides and P. sericea, which are currently named O. acuminatum, O. virgatum and O. sericeum respectively.

When Carl Thunberg, who visited the Cape from 1772 till 1775, revised Psoralea in 1823, and therein added P. tomentosa, P. racemosa, P. argentea and P. striata (now O. sericeum, O. racemosum, O. argenteum and O. striatum).

Ernst Heinrich Friedrich Meyer described in 1832 Psoralea obliqua (now Otholobium obliquum), P. bracteata var.

In 1836, Psoralea was reviewed by Christian Friedrich Ecklon and Karl Ludwig Philipp Zeyher, who distinguished P. albicans (= O. argenteum), P. algoensis and P. bracteolata (which are considered to be conspecific and are known today as O. bracteolatum), P. candicans (now O. candicans), P. cephalotes and P. stachyerum (both now included in O. stachyerum), P. hilaris (currently O. racemosum), P. polyphylla (now O. polyphyllum), P. rupicola (now included in O. striatum), P. uncinata (now O. uncinatum) and P. venusta (now O. venustum).

In the same year Meyer published a revision in which he distinguished P. carnea, P. obliqua, P. parviflora, P. triantha (now known as O. carneum, O. obliquum, O. parviflorum and O. trianthum respectively), P. cephalotes (= O. stachyerum), P. densa (= O. acuminatum), and P. spathulata (= O. mundianum).

He reassigned many species previously included in Psoralea to his new genus and described many new species since then: Otholobium pungens in 1981, O. rubicundum and O. pictum in 1982,[2] O. swartbergense in 1986,[5] O. accrescens, O. arborescens, O. dreweae, O. flexuosum, O. fumeum, O. incanum, O. lanceolatum, O. lucens, O. nigricans, O. nitens, O. prodiens, O. pustulatum, O. sabulosum, O. saxosum and O. spissum in 1989.

[7] Also in 1990, James Grimes proposed to include eight species that occur in the Andes mountains: O. brachystachyum, O. glandulosum, O. higuerilla, O. holosericeum, O. munyense, O. pubescens (originally Psoralea brachystachya, P. glandulosa, P. higuerilla, P. holosericea, P. munyense and P. pubescens), O. mexicanum (Indigofera mexicana) and the new species O.

[9] These two authors further described O. accrescens, O. dreweae, O. lanceolatum, O. lucens, O. nitens, O. piliferum, O. prodiens, O. sabulosum, and O. saxosum in 2017.

Like in many other plant genera, species density dramatically decreases to the east and north of the West Cape province.

[2] The species assigned to the genus by Grimes occur in the Andes from Chile in the south to Colombia and Venezuela in the north.

The survival of twenty-four taxa is considered to be of least concern: O. acuminatum, O. arborescens, O. bracteolatum, O. afrum, O. candicans, O. flexuosum, O. foliosum subsp.

gazense, O. fumeum, O. hirtum, O. mundianum, O. nigricans, O. obliquum, O. parviflorum, O. pictum, O. polyphyllum, O. polystictum, O. sericeum, O. spicatum, O. stachyerum, O. striatum, O. trianthum, O. virgatum, O. wilmsii and O. zeyheri.