P.D.F. Kok

Pollen types in the lauraceae

Abstract Pollen morphology of southern African Lauraceae (Cassytha, Cryptocarya, Dahlgrenodendron, Ocotea) and members of the genera Beilschmiedia, Eusideroxylon, Hypodaphnis, Lindera and Potoxylon was studied by means of light and scanning electron microscopy. Pollen morphologically the various genera could readily be distinguished from each other, but few interspecific differences were found. To assess the taxonomic significance of pollen characters in Lauraceae, evidence from the literature was also considered and compared with the infrafamilial classification proposed by Kostermans. On the basis of mainly shape and exine sculpture, four pollen types are distinguished in Lauraceae. Pollen type A (grains spheroidal, apolar, spinulose) has been only recorded in the tribes Perseeae, Cinnamomeae, Litseeae and Hypodaphneae; pollen type B (oblate/peroblate, isopolar, slightly to strongly verrucate) occurs only in the Cryptocaryeae; pollen type C (spheroidal, apolar, strongly verrucate/spinuloid) is character...

The genus Eugenia (Myrtaceae) in southern Africa: Structure and taxonomic value of wood

The anatomy of 60 samples of mature bark representing 12 southern African species of Eugenia s.str. was studied. Bark surface patterns are correlated with internal structure and the taxonomic significance of the bark features is explored. Two bark categories are distinguished. Bark type X [E. capensis (Eckl. & Zeyh.) Sond., E. natalitia Sond., E. simii Duemmer and E. umtamvunensis Van Wyk] is characterized principally by a smooth or weakly dippled-scaly surface, abundant dilatation tissue (pseudocortex) in the inner bark, phellem with one type of phelloid cell and a well-defined phelloderm. Bark anatomy was found to be useful to separate species. Bark type Y [E. erythrophylla Strey, E. verdoorniae Van Wyk, E. woodii Duemmer, E. zeyheri (Harv.) Harv., E. zuluensis Duemmer and three undescribed species] is characterized mainly by a flaky surface, little dilatation growth in the inner bark, phellem with two types of phelloids in the phellem and the lack of a distinct phelloderm. With the exception of E. zuluensis these species cannot be distinguished on the basis of bark features. Bark characters confirm a previously proposed distinction between two supraspecific groups among native species of Eugenia. For diagnostic purposes bark structure is more useful than wood. It is suggested that some of the differences between the two main bark types can be interpreted in terms of the relative rates of formation of xylem and phloem at the vascular cambium.

Studies on Digitaria (Poaceae) I. Enumeration of species and synonymy

A list of the species recognized in southern Africa is published. Several taxa recognized previously are reduced to synonymy.

Studies on Pavetta (Rubiaceae) II. Enumeration of species and synonymy

A list of the species recognized in southern Africa is published. Several taxa recognized previously are reduced to synonymy and a new combination is proposed.

Systematic study of Digitaria section Digitaria (Poaceae) in southern Africa

The section Digitaria Veldk. to which Digitaria sanguinalis (L.) Scop. belongs, is represented in southern Africa by five species. Two species namely D. acuminatissima Stapf and D. nuda Schumach., were not previously recorded from southern Africa. Characters traditionally employed to differentiate between species in this taxonomically difficult section were found to be useful to distinguish between the southern African species. These characters include the relative length of the upper glume and lower lemma, the absence of the lower glume, spiculate lateral veins of the lower lemma, arrangement of racemes, length of the ligule and pubescence of the lamina. The presence of secondary racemes and setae on the racemes was found to be variable in some of the species and the suggestion by some authors that they may be of diagnostic value cannot be justified.

Extension of the geographical range and notes on the diagnostic characters of Canthium suberosum (Rubiaceae — Vanguerieae)

The known range of Canthium suberosum Codd, a species previously thought to have a rather limited distribution in the Transvaal and Swaziland, has been considerably extended. A comparative study of the anatomy of the leaves and young stems as well as the pollen morphology and fruit and seed structure prove that a putative new species from Natal and Pondoland is conspecific with C. suberosum.

The identity of Pachystigma bowkeri (Rubiaceae, tribe Vanguerieae)

Since its publication the name Pachystigma bowkeri Robyns has not been taken up and various authors suggested that the taxon to which it was applied might be conspecific with P. macrocalyx (Sond.) Robyns. In a recent study of the genus in southern Africa it was established that P. macrocalyx constitutes a heterogeneous taxon. Two species should be recognized with P. bowkeri Robyns being the correct name for one of these. The name P. bowkeri Robyns is therefore reinstated.

Studies in Pavetta (Rubiaceae). III. Pavetta lanceolata and its allies (section Aethiopinymphe)

Since BremeKamp’s (1934) monograph of Pavetta L. (Rubiaceae) no taxonomic work in the genus has been undertaken in southern Africa. During a recent taxonomic revision of the genus in southern Africa, difficulties were encountered with species delimitation in some sections and the names Pavetta lanceolata Eckl. and P. tristis Brem. appear to have been misapplied. Three instead of six species are recognized in the section Aetniopinympne Brem. Characters employed to distinguish between the species in this fairly homogeneous section include the form and size of the calyx lobes, the size of the corolla, form and size of the lamina and the length of the petiole. A key to the species, the synonymy, diagnostic features and geographical distribution of each of the species are given.

Two varieties of Cussonia paniculata Eckl. & Zeyh. (Araliaceae)

An intensive study of Cussonia paniculata Eckl. & Zeyh. (Mountain Cabbage Tree) revealed that this species is represented by two varieties. C. paniculata Eckl. & Zeyh. var. paniculata is characterized by primary leaflets (pinnae) of which the margins are for the greater part entire and a few teeth are present, apically. The flowering system consists of biracemose spikes. In contrast, C. paniculata var. sinuata Reyneke et Kok var. nov. has sinuate primary leaflets and a flowering system usually consisting of umbellate racemose spikes.