Monday, February 24, 2020

[Botany • 2020] Combretum eugeneanum • A New Species of Combretum Sect. Ciliatipetala (Combretaceae) from South Africa

Combretum eugeneanum R.G.C.Boon, Jordaan & A.E.van Wyk

in Boon, Jordaan & van Wyk, 2020.

Combretum eugeneanum, a new species from northeastern KwaZulu-Natal, South Africa and confined to the Maputaland Centre of Plant Endemism, is described, illustrated, mapped, and compared with southern African members of the genus with which it may be confused. In a narrowly defined genus Combretum, the new species belongs to Combretum sect. Ciliatipetala. In herbaria, it has usually been confused with close relatives C. apiculatum and C. edwardsii, as well as several other more distantly related members of the genus, in particular C. woodii. The new species is also closely related to the recently described C. stylesii. It is readily distinguished as an essentially glabrous woody climber or scrambling shrub needing other vegetation for support, leaf apices rarely apiculate, tertiary veins raised on the adaxial leaf surface, inflorescences few-flowered and subcapitate, upper hypanthium cupuliform, flowers with orange-red centres (discs) and peltate scales comprised of essentially eight radial cells, most of which are subdivided by at least one tangential wall, the resulting outer and inner cell(s) often with at least one additional radial wall. Combretum eugeneanum grows in Sand Forest and associated sandy bushveld, and its range and habitat does not overlap with that of C. edwardsii or C. stylesii, both of which are also very often lianas.

Keywords: anatomy, Combretoideae, Combretum eugeneanum, endemism, Maputaland Centre of Endemism, peltate scales, scales, taxonomy, Eudicots

FIGURE 3. Combretum eugeneanum R.G.C.Boon, Jordaan & A.E.van Wyk.
A. Flowering branchlet. B. Fruiting branchlet. C. Flower. D. Flower with half removed. E. Hair-tuft domatia in principal lateral vein axils of abaxial leaf blade surface. Scale bar = 10 mm (A & B), or 1 mm (C–E). A based on Ward 2644, B based on Moll 5632, C based on Ward 2661, D based on Moll 4359. Artist: Daleen Roodt.

FIGURE 1. Combretum eugeneanum R.G.C.Boon, Jordaan & A.E.van Wyk.
 A. Trunk of a plant reaching the Sand Forest canopy at False Bay Park, Hluhluwe. B. Flowers at Tembe Elephant Park; note orange-red disc. C. Fruiting branchlet at Ndumo Game Reserve. Photograph taken in March when samaras fully grown, but before drying during autumn and early winter. Note glutinous seed pod. Photographs: R.G.C. Boon.

Combretum eugeneanum R.G.C.Boon, Jordaan & A.E.van Wyk, sp. nov.,  

Diagnosis:— Closely related to Combretum apiculatum, but easily distinguished from this species by being a scrambling shrub to woody climber (vs. usually a single-stemmed tree up to 8 m tall with a rounded canopy), leaf apex acute to obtuse, sometimes acuminate, very rarely apiculate (vs. leaf apex always apiculate), inflorescence a few-flowered subcapitate spike of up to 15(–16) flowers, flowers compactly arranged (vs. an elongated many-flowered spike with about 25 flowers), upper hypanthium cupuliform (vs. campanulate), fruit 18–20 × 22–24 mm (vs. 20–30 × 15–25 mm), and scales of 8 radially arranged cells with most of these cells usually subdivided by at least one tangential wall, the resulting outer and inner cell(s) often with at least one additional radial wall (vs. usually simple 8-celled). Also related to C. edwardsii and C. stylesii; all three being scramblers or climbers, but the range of C. eugeneanum does not overlap and habitat differs. Older growth of the new species is almost totally glabrous, whereas C. edwardsii and C. stylesii have leaves, petioles and branchlets with dense hairs. Additionally, in C. edwardsii the red-brown scales are visible with the naked eye and the inflorescence is an elongated spike, whereas in C. eugeneanum the scales are invisible without magnification and the inflorescence is subcapitate.

FIGURE 2. Combretum eugeneanum, leaf and scale morphology.
A. Leaves, showing adaxial (top) and abaxial (bottom) lamina surfaces. Note the thin glutinous (shiny) secretion on the lamina surfaces and raised tertiary veins on the adaxial surface. B. Selection of scales (stained with Sudan IV) from leaves of the same collection (Ward 1970) to show variation in size, shape and number of cells. Scale bar in mm refers to leaves; one in µm to scales. Photographs: R.G.C. Boon (leaves) and A.E. van Wyk (scales).

FIGURE 5. Lepidoptera recorded on Combretum eugeneanum.
 A. Larva of the moth Desmeocraera vernalis (family Notodontidae, subfamily Dicranurinae), hitherto only recorded as using members of Combretum as food plant.
B. Hairy larvae of a moth that probably belongs to family Erebidae, subfamily Lymantriinae, feeding on bark-growing lichens. It is not host-plant specific and larvae were also seen feeding on the bark of other tree species. Photographs: G. Lang.

Etymology:— The specific epithet honours Eugene John Moll (1941– ), eminent South African plant ecologist and author of books on tree identification. He has undertaken vegetation studies in, amongst others, KwaZulu-Natal, where he has collected many herbarium specimens from Maputaland, several of which turned out to be new records, or new taxa (Glen & Germishuizen 2010).

Common names:— Maputaland climbing bushwillow; maputalandrankboswilg (Afrikaans).

 Richard G.C. Boon, Marie Jordaan and Abraham E. van Wyk. 2020. A New Species of Combretum Sect. Ciliatipetala (Combretaceae) from South Africa. Phytotaxa. phytotaxa.434(1); 1–12. DOI: 10.11646/phytotaxa.434.1.1