Three subspecies of Pelargonium laevigatum ( Geraniaceae )

Pelargonium laevigatum (L. f.) Willd. is a variable species. The macromorphology, anatomy of the leaves, chromosome numbers and geographical distribution of the species were studied, and it is concluded that three subspecies should be distinguished. The subsp. diversifolium (Wendl.) Schonken stat. nov. and subsp. oxyphyHum (DC.) Schonken stat. nov. were originally described as species. A key to identify the three subspecies, a distribution map. and illustrations o f the macromorphological characters as well as anatomical features of the leaves, are provided.


INTRODUCTION
Harvey (I860) described the section Glaucophyllum and recognized Pelargonium laevigatum (L.f.) Willd.as one of the species in the section.Van der Walt et al. (1990) altered the composition of the section Glaucophyllum but concluded that P. laevigatum should remain in the section.P. laevigatum is a variable species and Schonken (1980) suggested that three subspecies should be distin guished.For this study the macromorphology, leaf anat omy, chromosome numbers and geographical distribution of the species have been studied to determine whether it is justified to recognize infraspecific taxa.

MATERIAL AND METHODS
For the morphological and geographical distribution studies, specimens of altogether 17 herbaria were studied.This was followed by extensive field work on different populations in the entire distribution area, mainly to de tenu ine the variation in morphological features.
Transverse sections, 12-15 |im thick, of wax-embed ded terminal leaflets and petioles were cut with a rotary microtome and stained with Alcian Green-Safranin (Joel 1983).The sections were made through the middle part of the terminal leaflets and petioles.For mitosis, root tips were treated with 0.002 mol 8hydroxiquinoline for 24 h at 20:C.fixed in 3:1 absolute ethanol and glacial acid, and stained with aceto-carmine.

Diagnostic anatomical features o f leaves
Petiole: cordiform in transverse section, glandular hairs multicellular, non-glandular hairs unicellular, hypodermis not clearly differentiated, parenchymatous cortex 4 -6 lay ers, extraxylary sclerenchyma cylinder continuous and 2-4 layers wide, main vascular bundles 4. smaller bundles 2-6, medullary bundle usually lacking (Figure 2A).Lam ina: V-shaped to more or less flattened in transverse sec tion, trichomes as on petiole, stomata evenly distributed in ad-and abaxial epidermis, mesophyll not clearly dif ferentiated in palisade and spongy parenchyma, 2 adaxial palisade layers larger than 1 abaxial layer (Figure 3A).Subsp.laevigatum occurs in the southern and eastern Cape, and it is known from Rooiberg near Calitzdorp, east wards to Otterford Forest Reserve near Port Elizabeth (Figure 4).It has been collected from 180 m above sea level near Humansdorp to 1 600 m in the Swartberg Range.The rainfall in its distribution area varies from 200-600 mm per annum.Subsp.laevigatum is morphologically very variable but a continuous variation pattern makes it impossible to di vide it into different taxa.Varying characters are the number of flowers per pseudo-umbel and the size of the petals, as well as the indumentum and degree of incision of the leaf margins.To complicate matters, there seem to be natural hybrids between subsp.laevigatum and Pelar gonium fruticosum (Cav.)Willd.P laevigatum depicted in Van der Walt & Vorster (1981) with greenish leaves is most probably an example of such a hybrid.These sus pected hybrids occur in the Swartbei^ Pass where subsp.laevigatum and P. fruticosum are common.
The plants occurring at Boschberg near Somerset East have finely divided leaves superficially resembling those of P fruticosum.This form was described by Bolus (1890) as P macowanii and quoted by Knuth (1912) as P. divaricatum (Thunb.)DC. var.scabrum Harv.However, the glaucous leaves and floral characters of these plants are typical of P. laevigatum and we concluded that they rep resent a form of subsp.laevigatum.The atypical leaves are probably the result of the local environmental condi tions and geographical isolation.Some plants growing in Long Kloof (Fourcade 2704) and in the Otterford Forest Reserve ( Wilman 1109) have up to five flowers per pseudo-umbel and the petals are exceptionally large.The pinnae of these plants are also relatively wide.Geranium trifoliatum Andr.: (1805).Pelargonium trifoliatum (Andr.)Sweet: 294 (1826).Iconotype: Andrews, Geraniums c. ic.(1805).

Diagnostic anatomical features o f leaves
Petiole: adaxially flattened, glandular hairs multicellular, non-glandular hairs unicellular, hypodermis clearly differen tiated, parenchymatous cortex 5 -6 layers, extraxylary sclerenchyma cylinder continuous and 2-6 layers wide, main vascular bundles 4, smaller bundles 4-8, medullary bundle 1 or 0 (Figure 2B).Lamina: flattened, trichomes as on petiole, more stomata abaxially, mesophyll differentiated in palisade and spongy parenchyma, 2 adaxial palisade layers larger than 1 abaxial layer (Figure 3B).Subsp.diversifolium occurs from Gydouw near Ceres eastwards to the Robinson Pass between Oudtshoom and Mossel Bay (Figure 4).It is often found in mountainous habitats in a variety of vegetation types.Its distribution area falls entirely in the winter rainfall region, but it usu ally occurs on the lower slopes of mountains or on hills where the rainfall is relatively low in comparison to habi tats higher up on the mountains.

Diagnostic anatom ical features o f leaves
Petiole: ad axially flattened to cordiform , w ithout trichomes, hypodermis not clearly differentiated, paren chyma cortex 5 -6 cell layers, extraxylary sclerenchyma cylinder continuous and 2-5 layers wide, main vascular bundles 4, smaller bundles 6 -8, medullary bundle 1 or 0 (Figure 2C).Lam ina: more or less flattened to centric, more stomata abaxially, mesophyll differentiated in pali sade and spongy parenchyma, 1 adaxial palisade layer larger than 2 ahaxial layers, mesophyll in centric leaves not clearly differentiated (Figure 3C, D).The phenoplasticity of the species is also reflected in the leaf anatomy.The leaflets of subsp.oxyphyllum for example vary from flattened to centric.A medullary vascular bundle can be present or absent in the petioles o f all three subspecies, even in different leaves of the same plant.The occurrence of hairs on the leaves of subsp.laevigatum is also extremely variable.Anatomical features o f the leaves of P. laevigatum are therefore of limited taxonomic importance.We are indebted to Prof. Dr Focke Albers for assisting us to determine the chromosome numbers and the Brenthurst Library (copyright) for permission to reproduce the water-colour paintings by Ellaphie Ward-Hilhorst.