J.J.A. van der Walt

Untersuchungen zur Karyologie und Mikrosporogenese vonPelargonium sect.Pelargonium (Geraniaceae)

The chromosome numbers of the 24 species of sect.Pelargonium were determined from field collected and cultivated plants of known localities in S. Africa. Twelve species are diploid (2n = 22), eight tetraploid (2n = 44), one hexaploid (2n = 66), and three octoploid (2n = 88). The chromosome numbers correlate well with the proposed subdivision of sect.Pelargonium. Its chromosomes are relatively small (1.0–1.5 µm) in comparison to most of the other sections, and its diploid karyotype is considered to be primitive. The occurrence of the basic number x = 11 in this section, in other sections of the genus, and in related genera (Monsonia, Sarcocaulon) leads to the conclusion that x = 11 probably is basic for the whole genus. — The pollen meiosis, microsporogenesis and pollen fertility of the diploid species is normal, with the exception of one, possibly young taxon from the Greyton Nature Reserve. The tetraploid species could be of autoploid origin, the higher polyploids exhibit a mixed auto-alloploid nature. — The 20 diploid and tetraploid species have a relatively small distribution range, most of them occur in the SW. Cape Province of South Africa. This area may therefore be considered as the centre of origin of the genus. Three of the four high polyploid species occupy rather large areas.

A model for species-area relationships in plant communities

A model is proposed for the fitting of species-area curves to data from the Stellenbosch region, South Africa. Basic assumptions of the model are finiteness of the number of species in a finite area, and random distribution of plant species over the region. The model involves a distribution of densities of different species, and the parameters of this distri- bution are useful for describing and classifying communities. The data of the Stellenbosch region suggest that the assump- tions of the model break down in areas greater than 500 m2.

A taxonomic revision of Pelargonium section Campylia (Geraniaceae)

A multidisciplinary approach was followed in this revision of the section Campylia (Sweet) DC. In addition to macromorphology, the leaf anatomy, pollen morphology and chromosome numbers were studied to delimit the taxa and determine their relationships. Seven species and five subspecies are recognized. Two new subspecies, P. caespitosum Turcz. subsp. concavum Hugo and P. ovale (Burm. f.) L’Herit. subsp. hyalinum Hugo, are described. The status of P. ovale var. veronicifolium (Eckl. & Zeyh.) Hanv. is raised to subspecific rank as subsp. veronicifolium (Eckl. & Zeyh.) Hugo. It is concluded that the section Campylia is advanced and probably derived from the section Pelargonium DC.

Observations on the pollination of Pelargonium tricolor, section Campylia (Geraniaceae)

A group of four species of Pelargonium L’Herit. in the section Campylia (Sweet) DC. have embossed ‘warty areas’ at the bases of the posterior petals of the zygomorphic flowers. In Pelargonium tricolor Curt, these embossed areas are most distinctive. The significance of these embossed areas in the attraction of insect pollinators is discussed. From repeated observations of P. tricolor it is concluded that these areas are false nectaries and that they are effective in attracting dipteran pollinators. Megapalpus capensis Wiedemann (Diptera: Bombyliidae), in particular, exhibits strong association with these false nectaries. It is further predicted that the embossed areas on the petals of the remaining three species in the group, namely P. capillare (Cav.) Willd., P. ocellatum J.J.A. van der Walt and P. incarnatum (L’Herit.) Moench have similar value for attracting anthophilous insects.

Origin of the rose-scented Pelargonium cultivar grown on Réunion Island

The Pelargonium cultivar grown on Reunion for the production of rose-scented geranium oil is locally known as the cv. Rose. The origin of the cv. Rose is demonstrated by comparing its morphology, chromosome number and essential oil with those of putative ancestral species. It is concluded that P. capitatum (L.) L’Herit. and P. radens H.E. Moore can be considered as the parent species. A comparison of the characters of the cv. Rose and those of artificial hybrids between P. capitatum and P. radens , confirmed the assumption.

Pelargonium tomentosum: A potential source of peppermint-scented essential oil

A synopsis of the nomenclature and morphological features of Pelargonium tomentosum Jacq. (2n=44) is presented. The structure of the trichomes is described in detail and the composition of the essential oil is tabulated. The main components of the essential oil are (-)-isomenthone (61–62%) and (+)-menthone (25–27%), the rest being terpenic hydrocarbons. It is concluded that P. tomentosum has the potential to become a new crop plant for the production of natural peppermint-scented essential oil in South Africa.

A taxonomic revision of the section Myrrhidium of Pelargonium (Geraniaceae) in southern Africa

A multidisciplinary approach was followed in this revision of the section Myrrhidium DC. Besides the morphology, the anatomy of the leaves, pollen and chromosomes were studied in order to delimit the taxa and to determine their relationships. Six species, six subspecies and four varieties are recognized. P. longicaule Jacq. var. angustipetalum Boucher is described as a new taxon and several new combinations are made. The diagnostic features of the section are the heteroblastic leaves, extremely zygomorphic flowers with prominently raised veins on the sepals, four to five petals and five or seven fertile stamens. The floral structure indicates that the section Myrrhidium is an advanced one and that it is closely related to the section Jenkinsonia (Sweet) Harv.

Composition of the Essential Oil of Pelargonium vitifolium (L.) L'Hérit. (Geraniaceae)

ABSTRACT The essential oil of several natural populations of P. vitifolium was analyzed by GC and GC/MS. The main constituents found were citronellic acid (77–85%) and 10-epi-γ-eudesmol (5%).

A biosystematic study of Pelargonium section Ligularia: 1. A new section Subsucculentia

The presumed relationship between P. grandicalcaratum Knuth, P. karooicum Compton & Barnes, P. otaviense Knuth and P. spinosum Willd., based on karyological characteristics, is confirmed by macromorphological, palynological, rbc L gene sequence studies and an analysis of phenolic compounds. These four species form the new section Subsucculentia J.J.A. v.d. Walt. Taxonomic treatments of the section and species are presented.

A biosystematic study of Pelargonium section Ligularia: 3. Reappraisal of section Jenkinsonia

The presumed relationship between P. antidysentericum (Eckl. & Zeyh.) Kostel., P. divisifolium Vorster, P. dolomiticum Knuth, P. griseum Knuth, P. plurisectum Salter, P. praemorsum (Andr.) Dietr., P. redactum Vorster, P. seneciodes L’Herit., P. tenuicaule Knuth, P. tragacanthoides Burch, and P. trifidum Jacq., based on karyological characters, is confirmed by palynological and rbc L gene sequence studies as well as phenolic compounds. These 11 species are placed in the section Jenkinsonia (Sweet) DC. ampl. J.J.A. van der Walt. The big variation in floral structure in the section is ascribed to convergent evolution and different pollination strategies. Taxonomic treatments of the section and species are presented.