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Melocactus intortus is a species of strongly dimorphic plants whose different parts show strong correlations between structure and function. Each individual has one unbranched monopodial shoot; during the first several years of life, this grows as a photosynthetic juvenile with a transparent epidermis, numerous stomata and a system of cortical bundles that permeate the chlorophyllous outer cortex. Cortical bundles undergo secondary growth. The xylem of the stele contains wide vessel elements, vascular tracheids and fibres, resulting in a wood that is probably relatively strong and efficient at water conduction. After several years, the plant undergoes a transition to being adult and all further shoot elongation growth results in a region of body with different anatomy and which is capable of flowering, the cephalium. The epidermis is thin, lacks stomata and is soon converted to a cork cambium. The cortex is nonphotosynthetic and cortical bundles do not have secondary growth. The wood of the adult portion contains only narrow vessels and parenchyma. The juvenile and adult portions of each shoot have distinct functions as well as distinct requirements for gas exchange; water and nutrient transport; and mechanical strength. When interpreting the selective value of the various anatomical features, it is critically important to consider the specific role and requirements of the particular portion of the plant in which they occur.
Generic limits and relationships in tribe Cereeae are reviewed and reassessed using cladistic methodology. Based on field and herbarium studies, and on reliable published observations, 20 characters are discussed in detail, polarized into plesiomorphic (primitive) and apomorphic (derived) states and then employed in the generation of a series of phylogenetic hypotheses using the PAUP computer program. Melocactus, Coleocephalocereus (incl. subg. Buiningia but excl. subg. Lagenopsis), Micranthocereus and Austrocephalocereus (excl. Espostoopsis dybowskii) represent a monophyletic group, here provisionally designated subtribe Melocactinae F. Buxbaum, and defined by the following synapomorphies: (1) loss of well-developed stem wood, (2) sunken-lateral or terminal cephalium, (3) nonblackening floral remains, and (4) derived fruit apex morphology (superficial floral remains). Uebelmannia, whose placement in tribe Cereeae is at best provisional, may also belong to this group, unless its similarities are due to convergence. Coleocephalocereus and Austrocephalocereus lack obvious autapomorphies distinguishing them from Melocactus and Micranthocereus, respectively. The superficial pseudocephalium present in most species of Micranthocereus may have been derived from the sunken-lateral type characteristic of this group. The remaining genera of the tribe, i.e. the Cereinae Britton & Rose, are more loosely related with relatively few synapomorphies. Pilosocereus sens. str. (incl. Pseudopilocereus) is clearly defined by the apomorphies of loss of well-developed stem wood (in parallel with the Melocactinae) and more or less depressed, dehiscent fruits (fruit dehiscence evolved in parallel in Cereus sens. lat.). ‘Lagenopsis’ (Cereus luetzelburgii) may have common ancestry with Stephanocereus, which is allied to Arrojadoa by the synapomorphic ring cephalium. Assessment of the precise relationship and appropriate classification (rank) of these three taxa, and a potentially related but inadequately known undescribed species, must await more comprehensive data, since at present it is not possible to be certain whether they have had a close common ancestry or are in part the product of convergence. Espostoopsis dybowskii is inadequately known, but does not appear to belong in Austrocephalocereus or Melocactinae; it may even be out of place in Cereeae (cf. Trichocereeae, especially Espostoa). Brasilicereus has no synapomorphies with, and various autapomorphies distinguishing it from, Cereus, and should be recognized as a genus. Cipocereus is defined by indehiscent fruits with colourless, watery pulp and should not be sunk into Pilosocereus. It is amplified to include Floribunda pusilliflora, Cereus crassisepalus and Pilosocereus bradei, besides C. minensis (C. pleurocarpus) and an undescribed species. Cereus sens. lat. (incl. subg. Ebneria, Mirabella minensis, Praecereus and Subpilocereus) is a primitive complex that cannot be resolved in terms of synapomorphies at present. Either of Cereus, Cipocereus or Brasilicereus—the genera with fewest synapomorphies—may be closest to the ancestor of the tribe. A key to the principal taxa of tribe Cereeae is provided.
This is the second instalment of an annotated list of Conophytum names, continued from Bradleya 6:101–120 (1988). Various neo- and lectotypes are designated and subg. Berris-fordia is sunk into Conophytum sect. Cylindrata.
Miscellaneous notes on Stapelieae (Asclepiadaceae). Part 7 deals with Caralluma staintonii Hara, and provides habitat information, amplified description and illustrations of this Nepalese species. Part 8 is concerned with new synonymy for Caralluma edulis (Edgew.)Benth., for which distributional data are included.
Sarcostemma pearsonii N.E.Br. is a little known species endemic to the northern Cape Province and Namibia. Its morphological and biological features are described in detail and compared with those found in the far more widespread members of the S. viminale complex.
This is the second part of a series of notes and new taxa supplementary to the author's The Genus Echinocereus (1985), continued from Bradleya 6: 65–84 (1988), and dealing with Mexican species in sections Reichenbachii, Wilcoxia and Pulchellus. E.pentalophus is transferred from sect. Echinocereus and allied with E. subinermis. The description of E. bristolii is amplified and var. pseudopectinatus elevated to specific rank. The circumscription of E. pulchellus varieties is revised and var. sharpii N.P. Taylor (var. nov.) from Nuevo Leon is described.
Ariocarpus fissuratus var. hintonii W. Stuppy & N.P. Taylor, from northern San Luis Potosí, Mexico, is described and compared with var. fissuratus. It differs from other forms of the species by its dwarf stem, narrower tubercles, smaller seeds and disjunct distribution. A. fissuratus var. lloydii is linked to var. fissuratus by populations intermediate in character. A key to the three varieties of A. fissuratus is provided.
A new species, S. tricae D. Hunt, and new sectional names in Selenicereus (A. Berger) Britton & Rose are proposed. The name S. sect. Salmdyckia D. Hunt is proposed for the species hitherto referred to Mediocactus B. & R., since neotypification of Cereus coccineus Salm-Dyck ex De Candolle renders the name Mediocactus a synonym of Heliocereus B. & R. S. rizzinii Scheinvar is treated as a synonym of S. setaceus (‘Mediocactus coccineus’ auctt.). Reasons for recognizing two species only in Aporocactus Lemaire are given and Lemaire's etymological explanation for the generic name re-stated.