Trichocereeae

Abstract: In this study, we investigated the effect of light regimen (white light vs. darkness) on the germination of 12 species of the Echinopsis genus (tribe Trichocereeae, Cactaceae). This genus presents a variety of growth forms and relatively small and uniform seed size. These traits allowed us to test, within the same linage and removing seed mass effect, the hypothesis that the germination response to light (indifferent to light or positive photoblastic) is related to growth form. Our results reject this hypothesis since no seeds germinated in darkness, so all of the species can be classified as being positively photoblastic. The proportion of seed germination with white light was significantly different among cactus growth forms. Columnar cacti (arborescent, creeping and short) showed a greater proportion of seed germination than barrel and globose cacti. The germination rate differed among growth forms and species. At constant temperatures, creeping columnar cacti presented a significantly higher germination rate than the other growth forms. With alternating temperatures, columnar cacti showed higher germination rates than the other growth forms. The low proportion of seeds that germinated for some species indicates that they show seed dormancy. Our results suggest that germination responses to light in the cactus family could be related to seed mass and phylogenetic constraints.

Abstract: 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.

Abstract: The phylogenetic distribution of two deletions, of about 350 and 250 bp respectively, within the chloroplast trnT–trnL intergenic spacer was examined. One deletion was found in all members of Cactaceae subfamily Cactoideae sampled, totaling 37 species, but not in taxa from other subfamilies or closely related families. The second was shared by a subset of Cactoideae comprising members of tribes Cereeae, Trichocereeae, and Browningieae (in part), as well as Harrisia. Close links among the former three South American tribes have been previously hypothesized. This distribution suggested that Browningieae, a tribe defined largely by shared primitive features, were not monophyletic, and that Harrisia may have been incorrectly placed outside the Browningieae–Cereeae–Trichocereeae group.

Abstract: Chromosome numbers for a total of 54 individuals representing 13 genera and 40 species of Cactaceae, mostly in tribe Trichocereeae, are reported. Five additional taxa examined belong to subfamily Opuntioideae and other tribes of Cactoideae (Browningieae, Pachycereeae, Notocacteae, and Cereeae). Among Trichocereeae, counts for 35 taxa in eight genera are reported, with half of these (17 species) for the genus Haageocereus. These are the first chromosome numbers reported for 36 of the 40 taxa examined, as well as the first counts for the genus Haageocereus. Both diploid and polyploid counts were obtained. Twenty nine species were diploid with 2n=2x=22. Polyploid counts were obtained from the genera Espostoa, Cleistocactus, Haageocereus, and Weberbauerocereus; we detected one triploid (2n=3x=33), nine tetraploids (2n=4x=44), one hexaploid (2n=6x=66), and three octoploids (2n=8x=88). In two cases, different counts were recorded for different individuals of the same species (Espostoa lanata, with 2n=22, 44, and 66; and Weberbauerocereus rauhii, with 2n=44 and 88). These are the first reported polyploid counts for Haageocereus, Cleistocactus, and Espostoa. Our counts support the hypothesis that polyploidy and hybridization have played prominent roles in the evolution of Haageocereus, Weberbauerocereus, and other Trichocereeae.