Microloma is a small genus of about 10–12 species of flowering plants in the family Apocynaceae (order Gentianales), endemic to southern Africa and concentrated in the fynbos and arid scrub of South Africa, with a few species reaching Namibia. The genus was established by Robert Brown in 1809 and originally placed in the family Asclepiadaceae; it is now treated as part of the subfamily Asclepiadoideae within Apocynaceae.
Members of Microloma are herbaceous perennials taking two growth forms: slender twiners that scramble through surrounding vegetation in the manner of Ceropegia, and compact twiggy shrublets. Unlike many relatives in Asclepiadoideae, Microloma species produce clear sap rather than milky latex. Leaves are opposite, simple, and usually sessile. The flowers are borne in umbel-like cymes and are the genus's most distinctive feature: five waxy petals — typically brilliant red or reddish, occasionally yellow, orange, or pink — form a pentagonal, urn-shaped or oblong corolla tube whose interior carries tufts of downward-pointing hairs. The petals are arranged spirally and nearly close the tube mouth, concentrating nectar at the base. The anthers are sagittate and bear pollinia.
Flowers produce copious nectar — early botanist Rudolf Marloth noted that a drop could be shaken from each bloom in the morning — and the primary pollinators are sunbirds, to whose tongues the pollinia adhere in a specialised mutualism. Small moths and butterflies visit the flowers but are considered incidental. Many species develop a fascicle of fleshy storage roots around the base of the stem, allowing the plant to shed shoots and leaves during drought or after fire and re-sprout from the root reserve.
Notable species include M. sagittatum, whose root infusion has been used in traditional medicine to relieve abdominal pain, and M. tenuifolium, a common representative of arid Western Cape habitats. M. armatum (formerly M. massonii) is a densely branched shrublet with spine-tipped branches colloquially called "ystervarkbossie" (porcupine bush) in Afrikaans.
Etymology
The genus name Microloma was coined by Robert Brown in his 1809 publication Memoirs of the Wernerian Natural History Society (1: 53). Afrikaans common names reflect the plant's characteristics: "melktou" (milk-string, despite the absence of latex), "bokhorinkies" (little goat-horns, for the horn-shaped fruit), and "suikerkannetje" (little sugar-can, for the nectar-filled flowers).
Distribution
Microloma is predominantly South African, with most species confined to the Western Cape fynbos biome and adjacent arid karoo scrub. Several species (M. hereroense, M. namaquense, M. penicillatum, M. poicilanthum, M. longitubum) extend north into Namibia, including Damaraland.
Ecology
Microloma occupies arid scrub and fynbos habitats. Flowers produce abundant nectar and are primarily pollinated by sunbirds, which carry pollinia on their tongues — a striking example of specialised mutualism. Many species survive seasonal drought and veld fires by storing reserves in a fascicle of fleshy roots at the stem base, from which the plant can re-sprout after losing its aerial parts.
Cultural Uses
An infusion prepared from the fleshy root fascicle of Microloma sagittatum has been used in traditional medicine to relieve griping abdominal pain; the infusion is red in colour, and the root may be chewed directly when water is unavailable. Country children in South Africa historically sucked sweet nectar directly from the flower clusters of some species.
