Uncarina (2002)

By Lillian Giessow (July 2002)

The genus Uncarina is endemic to Madagascar and in the family Pedaliceae. The sesame seed plant is probably the best known member of this family, which resides in the genus Sesamum. Many species in Uncarina were once in the genus Harpagophytum, and the genera have many similarities, but most uncarinas are shrubby and most harpagophytums (“claw-plant” in Latin) are perennial herbs.

In their native environment, uncarinas are xerophytic shrubs to small trees with a somewhat swollen base. Their thick, soft branches have large deciduous, alternate, hairy leaves that vary in shape by species. Large lateral, zygomorphic flowers bloom in different colors that vary by species.

Uncarina fruits are indehiscent capsules covered with stout barb hooks which function in dispersal by catching on large animals. Indigenous people of Madagascar use the fruits from several species of Uncarina and Harpatophytum as mousetraps!

There are nine native species in the genus Uncarina in northern, western and southwestern Madagascar. U. petlata, with its golden-yelow flowers, is the most widespread. U. perrieri has completely golden-yellow flowers. Yellow-orange flowers are found on U. sakalava, and U. abbreviata has bright rose or purple blooms. U. decaryi is also widespread with golden-orange flowers. With yellow blooms, U. grandieri is closely related to and grows in the same areas as U. decaryi, but with a limestone soil.

U. leandrii has orange-yellow flowers and grows only in sandy soil. The rarely cultivated U. leptocarpa is the only species with pure white flowers. U. stellulifera flowers are rose-violet.

The U. roeoesliana appears to be closely related to the U. decaryi and U. grandieri. It is a newly described (or is it a non-native cultivar?) species which produces yellow flowers that are the smallest found on Uncarina. This very decorative species flowers while still young.

I purchased an Uncarina roeoesliana at the HSCSS show last year. It had finished blooming, but had two fruit pods. This past spring, Pam Schnebelen bravely cut open a tough, barbed seed pod to find its treasure of over 20 seeds. To our delight, we have each been able to start seedlings from them.
Pam’s, of course, are more robust than mine. She sowed hers on April 10. Her largest seedling has a stem about 3/4 inch high and eight leaves. Her smallest is a bit less than half as large. My seedlings seem to be about the size of her smallest seedling.

The original plant is slowly getting its summer leaves. I hope it produces more flowers and fruits this summer. My husband has been keeping caged field mice in the garage, and I may need the fruit to keep them out of the house!

Information for this article was gathered from Succulent and Xenophytic Plants of Madagascar, Volumes 1 and 2, by Werner Rauh, 1998, and The Plant Book, by D. J. Mabberley, 1997.