Two new Plectranthus species ( Lamiaceae ) and new distribution records from the Pondoland Centre of Plant Endemism , South Africa

Two newly discovered species of Plectranthus L'Hér. are described from the Pondoland Centre of Plant Endemism, on the eastern seaboard of South Africa. P. hrevimentum and P. stylesii are exceedingly narrow endemics known only from their type localities. The known distribution ranges of two other narrow endemics of the region. P. emstii and P. praetermissus, are expanded with new distribution records.


INTRODUCTION
The genus Plectranthus L'Hér.shows high levels of diversity along the eastern seaboard of South Africa.Speciation in the Pondoland Centre of plant diversity is espe cially pronounced and is probably the product of stable for est refugia which existed in the deep gorges that slice through the weather-resistant sandstones of the Msikaba Group [South African Committee for Stratigraphy (SACS) 1980].Their stability is probably mediated by the maritime climate.These gorges are flanked by seasonal sourveld grasslands of high productivity (and the correlated incidence of seasonal fire).Part of the diversity of herbaceous forest species is driven by the truncation of forest habitat and ensu ing allopatric speciation which contributes to one of the most important centres of plant diversity and endemism in Africa (Davis et al. 1994).The inability of many Plectranthus species to escape these enclaves is the product of desiccation intolerance, susceptibility to fire and the lack of long dis tance dispersal.This suite of limitations makes the subgenus Plectranthus a prime candidate for allopatric speciation and consequently the concentration of neo-endemic species in the Pondoland Centre is not surprising (Van Jaarsveld & Edwards 1991. 1997;Van Wyk & Smith 2001).flowered; verticels often alternately 3-and 6-flowered; rhachis rubro-strigose; lower bracts persistent, elliptical, 8-12 x 4-6 mm.upper bracLs lanceolate.3-4 x 0.5-1.0mm.rubro-punctate above, rubro-strigose and rubro-punc tate below; margins entire, rubro-ciliate; pedicels purple, 4-5 mm long.Calyx green to purple, sparsely rubrostrigose and rubro-punctate; upper sepal ovate.4.0-4.5 x 2.5-3.0 mm; lower sepals fused.5 mm long, lobes lanceo late, 3 mm long; tube 2-3 mm long.Corolla 25-30 mm long; tube laterally compressed.10-12 x 3.5-4.0mm, white with dense erect glandular trichomes; upper lip 4lobed.obtrullate 9-10 x 11-12 mm.white with 2 deep magenta central nectar guides, sparsely glandular-strigose outside, lateral auricles 4 mm long; lower lip navicular.4 mm long, dark pink, sparsely glandular.Stamens 4; fila ments free, 2-3 mm long, adnate to corolla throat.Style white, filiform.13 mm long; stigma purple, shortly bifid, upper lobe 1.0-1.5 mm long, lower lobe 0.5 mm long.Nutlets glabrous.Flowering time: January to March. Figure 1.This species is only known from material collected by David Styles during a joint botanical expedition to the Lupatana River Gorge in the Eastern Cape (Figure 2).Vegetative material was grown at the University of KwaZulu-Natal Botanical Gardens from w hich the flow ering type specimens were derived.

Plectranthus hrevimentum
Plants occur in steep sandstone gorges and flower in late summer.The short lower lip.from w hich the specif ic epithet is derived, and the broadly obtrullate upper lip are distinctive characteristics (Figure 1) seen also in Plectranthus hilliardiae Codd.
Plectranthus stylesii strongly resembles P. verticillatus but is distinguished from this procumbent species by its thick, rigid, erect stems and bushy habit; plants grow up to 0.6 m tall without support from adjacent vegeta tion.The leaves of P. stylesii are much larger (50-80 x 40-80 mm) than those of P verticillatus (16-40 x 12-40 mm).The corolla of the new species is distinctly con stricted at the throat, whereas that of P. verticillatus is only slightly narrowed.
Plectranthus stylesii is known only from the Msikaba River Gorge (Figure 2) where it grows in rocky forested habitats.

Plectranthus ernstii
Plectranthus ernstii Codd was described in 1982 from material collected at Oribi Gorge (Van Jaarsveld 3812) and the species was presumed to be an endemic to that gorge system, rather like P. oribiensis Codd.This assumption seemed plausible due to the succulent, aerial stems of the species which appear to be susceptible to burning.Recent collections, however, extend the known distribution of P. ernstii to Umtamvuna Gorge (Potgieter 85) and to Msikaba River (Edwards 3221).It seems probable that the species occurs in the intervening gorge systems as well (Figure 4).

Plectranthus praeterm issus
Plectranthus praetermissus Codd was described in 1979 after a number of localized collections had been made in the moist subtropical forests which surround Port St Johns.Recently, large populations of P. pratermissus were recorded from the Sakombe Forest near Mbotyi (Edwards & Potgieter 3248) (Figure 4).Here the species occurs in shallow lithosols in south-facing scarp forest in seasonally dry niches.