Leucadendron spissifolium subsp. oribinum I.Williams is a subspecies of flowering shrub in the family Proteaceae, commonly known in English as the Oribi spear-leaf conebush (Afrikaans: Oribigeelbos). It is one of five recognised subspecies of Leucadendron spissifolium (the spear-leaf conebush) and forms part of the fynbos and related grassland vegetation of southern Africa. The plant is native to South Africa and is regarded as threatened.
Taxonomy
The taxon was described by the botanist I. Williams and is cited as Leucadendron spissifolium (Salisb. ex Knight) I.Williams subsp. oribinum I.Williams. It belongs to the genus Leucadendron within the family Proteaceae. The species L. spissifolium was first described in 1809 under the name Euryspermum spissifolium and was transferred to Leucadendron in 1967. Five subspecies are generally recognised: subsp. spissifolium, subsp. fragrans, subsp. natalense, subsp. phillipsii, and subsp. oribinum.
Sources note that the extensive overlap of subsp. natalense and subsp. oribinum without observed hybridisation or intermediate forms has been interpreted as evidence that the two may warrant recognition as separate species; this remains a taxonomic observation rather than an established reclassification.
Description
Leucadendron spissifolium subsp. oribinum is a shrub that grows to approximately 0.5–1.5 m in height and produces many stems arising from a persistent rootstock. The plants are dioecious, meaning that male and female flowers are borne on separate individuals.
The leaves are spear-shaped and twisted at the base. The subspecies is distinguished from other subspecies of L. spissifolium by its sickle-shaped (falcate), more crowded leaves, which grow up to about 45 mm long in female plants and about 31 mm long in male plants. The male flowerheads are leafless and borne solitarily at the ends of short, slender branches, and are produced in numbers, giving off a faint smell of honey and yeast. The female flowerheads are also terminal and solitary. The flowers are yellow.
It belongs to a group informally called the "sunshine conebushes", which are characterised by winged seeds and smooth leaves, in contrast to the closely related "clay conebushes", which have rough leaves.
Distribution and habitat
The subspecies is a South African endemic, recorded from the Eastern Cape and KwaZulu-Natal provinces, where it occurs from the Oribi Plain and Oribi Gorge near Port Shepstone to Mkambati. Its total range spans roughly 106 km. This places it far from the Western Cape, where most species of Leucadendron occur and where the genus has its centre of diversity in the Cape Fold Mountains.
It grows in Pondoland coastal grassland (Pondoland-Ugu Sandstone Coastal Sourveld), on steep, stony, grassy slopes above cliffs, in sandy or loamy soil. Reported altitudinal ranges vary between sources: an altitude range of 80–500 m is given in the South African national red list assessment, while an older account cites 300–500 m.
Ecology
The subspecies is pyrophytic (fire-adapted). It survives fires by resprouting from underground boles or rootstocks, and it is thought to be long-lived, with a generation length suspected to exceed 100 years. Its fruits are serotinous: ripe seeds are retained in fire-resistant inflorescences in the canopy and released only after a fire. The seeds are winged and dispersed by wind.
The flowers are insect-pollinated, and flowering takes place in October and November, with fruits ripening several months later. In the wild the subspecies may begin flowering after about five years, though cultivated plants in England reportedly did not flower for more than seven years, possibly due to unsuitable environmental conditions.
Conservation
The subspecies is assessed as Vulnerable on the IUCN Red List (2020). Its South African national status is also Vulnerable, evaluated under the criteria A2c and B1ab(iii,v)+2ab(iii,v), with an extent of occurrence of roughly 1,057–1,341 km² and an area of occupancy of about 120–128 km², known from nine locations.
The principal historical threat has been habitat loss: at least 39% of its grassland habitat has been irreversibly modified, mainly for sugarcane, tea and banana cultivation and for urban development. This form of habitat conversion has largely ceased. Ongoing threats include degradation of remaining grassland through excessively frequent fires and unmanaged invasive plants; outside protected areas, grasslands are burned frequently to stimulate grazing for cattle.
The population trend is recorded as decreasing, with over 30% of the population suspected to have declined over the past 200 years (approximately two generations). Three large subpopulations are known, one of which — at Umtamvuna Nature Reserve — is thought to account for more than 80% of the known population. The subspecies is conserved within the Mkambati, Umtamvuna and Oribi Gorge Nature Reserves.
Etymology
The generic name Leucadendron is derived from the Greek leukos ("white") and dendron ("tree"), referring to the silvery foliage of the type species Leucadendron argenteum, the silver tree. The specific epithet spissifolium is described in source literature as referring to sticky leaves, while the subspecific epithet oribinum refers to part of the plant's distribution range at the Oribi Gorge in southern KwaZulu-Natal.
Notes
No significant economic exploitation of the subspecies is known. Its flowerheads have been noted as giving it potential as a garden plant, although specific cultivation requirements are not well established, and the species is reported to grow in damp places, implying a need for regular watering in cultivation.
