A revision of the genus Echidnopsis Hook.f. (Asclepiadaceae). The tropical north-east African and Arabian genus Echidnopsis is revised to include Pseudopectinaria. Nineteen species are recognised and they are grouped into four new sections. The new taxa E. scutellata subsp. dhofarensis and E. scutellata subsp. australis are published and four new combinations are made: E. scutellata subsp. planiflora, E. sharpei subsp. ciliata, E. sharpei subsp. repens, and E. malum. The following species are accepted: E. angustiloba, E. archeri, E. ballyi, E. bihendulensis, E. cereiformis, E. dammanniana, E. ericiflora, E. insularis, E. leachii, E. malum, E. mijerteina, E. montana, E. scutellata, E. seibanica, E. sharpei, E. squamulata, E. urceolata, E. virchowii, and E. watsonii. Descriptions, illustrations and distributional data are provided for all the taxa recognised.

Systematic anatomy of the primitive cereoid cactus Leptocereus quadricostatus. The genus Leptocereus is widely regarded as one of the most primitive of Cactaceae subfamily Cactoideae. It resembles the pereskias in having dense fibrous wood in its trunk and lower branches; this wood lacks vascular tracheids; it has septate protophloem fibres; and the ray cells are all thick walled and lignified. However, it also shows the beginnings of many features which are associated with the more advanced cacti: it has an enlarged, palisade cortex, a system of cortical vascular bundles, and medullary bundles. In addition, the wood of the uppermost portions of many branches is very parenchymatous, unlike the fibrous wood of the trunk. In some portions of the shoot, especially in the cephalia, the wood consists of just parenchyma and vessels, a trait which had been considered quite advanced. It seems reasonable that a strongly dimorphic plant such as Leptocereus would be able to give rise to the numerous diverse lines of evolution which exist in the Cactoideae.

The first part of a series of notes and new taxa supplementary to the author's The Genus Echinocereus (1985) is presented. The following new names, based on the results of studies in the field and of documented plants in cultivation, are published: Echinocereus cinerascens var. septentrionalis (var. nov.), E. cinerascens var. tulensis (stat. nov.), E. stramineus var. occidentalis (var. nov.), E. parkeri (sp. nov.), E. parkeri var. gonzalezii (var. nov.), E. rayonesensis (sp. nov ), E. longisetus var. delaetii (stat. nov.) and E. polyacanthus var. huitcholensis (stat. nov.). In addition, the circumscription of E. viereckii var. morricalii is substantially expanded, E. freudenbergeri is reinstated as a species, and E. knippelianus is tentatively referred to Sect. Echinocereus, E. viridiflorus Group. The grouping of species in Sect. Echinocereus is revised, and the descriptions of various species in Sections 1–4 amplified.

A brief commentary on the genera of tribe Cereeae is presented, with diagnoses of some genera, notes on the circumscription of subgenera and comments on several infrageneric and infraspecific taxa. A key to genera and a phylogenetic dendrogram are presented. Various new names in Cereus, Pilosocereus, Arrojadoa, Coleocephalocereus and Melocactus are published. Species relationships in Melocactus are briefly discussed.

The author introduces an annotated list of Conophytum names to be completed in about four instalments. Authorities, places of publication, details of typification and essential synonyms are cited for all bi- and trinomials listed. Accepted species are accompanied by a statement of their provisional infrageneric placement, a brief description, distributional data and discussion.