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There are several pitfalls when using DNA sequence data in classification of cacti or any other plants or animals. DNA sequence data has not and will not result in the “ultimate” cactus classification; it only provides additional characters by which phylogenies can be reconstructed. Only limited sequence data is currently available. Even if complete DNA sequences of all cactus species were known, we still could not fully use this data until we understand the mechanisms and tempos with which DNA sequences evolve.
Genome size (C-value) is used as a new criterion to investigate the taxonomy of the genus Aloe L. Nearly all species of the genus Aloe have the same basic chromosome number (2n = 2x = 14). However, the nuclear DNA content, measured in 83 species by flow cytometry with propidium iodide, is shown to range from about 16 to 44 pg in the diploids. This implies that the largest genome contains roughly 3 x 1010 more base pairs than the smallest. Therefore, nuclear DNA content is a very relevant taxonomic trait that can be measured simply by flow cytometry. It is shown that A. plicatilis (L.) Mill. and A. haemanthifolia A.Berger & Marloth have by far the lowest DNA content of all measured Aloe species and might belong to the same section. A. pillansii L. Guthrie has a DNA content similar to A. dichotoma Masson and the following new combinations are made: Aloe dichotoma Masson subsp. pillansii (L. Guthrie) Zonneveld comb. nov. and Aloe dichotoma subsp. ramosissima (Pillans) Zonneveld comb. nov. Aloe distans Haw. and A. comptonii Reynolds clearly belong to A. mitriformis Mill. and are combined here as: Aloe mitriformis Mill. subsp. distans (Haw.) Zonneveld comb. nov. and Aloe mitriformis Mill. subsp. comptonii (Reynolds) Zonneveld comb. nov.
Lawant & Winthagen (2001) proposed that a succulent Euphorbia, specifically E. resinifera, was portrayed about 1500 years ago, on page 149 of the monk-made parchment manuscript entitled Codex Neapolitanus. An alternative hypothesis, that the plant portrayed is a species of Caralluma, is here rejected. A full translation of the Greek text which accompanies the plant picture is also provided.
The shrubby mesemb species, Ruschia acutangula (Haw.) Schwantes, was recently rediscovered on the foothills of Jonaskop between Villiersdorp and McGregor, in the Western Cape Province of South Africa. The species has been lost to science for a long time, possibly since its first discovery more than 175 years ago. An emended description and its known distribution are provided here. The conservation status of R. acutangula is uncertain, and the species is probably threatened due to loss of habitat to farmlands and other developments.
The conservation value of two Soqotran endemic succulent plant species, Aloe perryi Baker and Duvaliandra dioscoridis (Lavranos) M. Gilbert, was assessed as part of a study of some aspects of their ecology.
A. perryi is important locally as a source of medicinal extracts and is harvested at some locations for export as well as local use. At one of the study sites this harvesting may be having an adverse affect on the local Aloe population. Other populations of A. perryi are not harvested or may be harvested only infrequently, but demand for the sap is increasing. A. perryi is widespread on the island, occurring mostly in scattered discrete populations. A. perryi should continue to be assigned to the conservation status category ‘Near Threatened’.
D. dioscoridis seems to be restricted to a single known population in one small area but appears to have a balanced population structure. Based on its restricted distribution D. dioscoridis should continue to be designated as ‘Critically Endangered’.
A large number of taxa of the genus Melocactus has been described from the islands of Aruba, Bonaire and Curaçao, which most recent authors have viewed as a single very variable species, M. macracanthos. A detailed field study and morphological analysis of the genus in Aruba suggests that three species are found on the island, M. macracanthos, M. stramineus and M. curvispinus subsp. koolwijkianus, together with a semi-stabilised hybrid M. x bozsingianus. The nomenclature has been revised with reference to type specimens, and the combination M. curvispinus subsp. koolwijkianus (Suringar)-Thomson is published as new.
Agave wercklei F.A.C.Weber ex Wercklé from Costa Rica is an attractive alien in frost-free areas of the south-east coast of South Africa where it has the potential of becoming a problem plant. In this contribution an amplified description of A. wercklei is given and the flowers and fruit are illustrated for the first time.
A facsimile of the original cactus plates and text from Plumier, Botanicon Americanum (1689–1697) is published for the first time. Analysis and identification of these plates is provided, together with an account of the life and travels of Charles Plumier (1646–1704).
Based on almost 1000 collections of species of Drosanthemum, the morphology, number of elements, and the changes during anthesis of flowers have been studied. Five main types of flowers are distinguished and described here: stamen carpet flowers, tall cone flowers, low cone flowers, low column flowers, and tassel flowers. A key to the types is given. In addition, one new species is described: D. dipageae H.E.K.Hartmann.