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A REVISION OF ARIOCARPUS (CACTACEAE). II. THE STATUS OF THE PROPOSED GENUS NEOGOMESIA
Abstract
Anderson, Edward F. (Pomona Coll., Claremont, California.) A revision of Ariocarpus (Cactaceae). II. The status of the proposed genus Neogomesia. Amer. Jour. Bot. 49(6): 615–622. Illus. 1962.—The proposed monotypic genus Neogomesia is found to be similar to Ariocarpus in seed structure, seedling development, habitat, certain significant internal characters, chemistry, flowers, pollen, and chromosomes. The reported differences in a reole structure and fruits are unfounded, if the developmental stages of each are considered. The presence of extensive mucilage-containing structures in Neogomesia is significant, because these structures have been reported previously only in Ariocarpus. Interspecific compatibility shows close genetic similarities between Neogomesia agavoides and the several species of Ariocarpus. The difference in structure of mature tubercles between Neogomesia and Ariocarpus is believed to be a variation in the location of growth and elongation with respect to the floriferous and spiniferous areolar areas. The author concludes that Neogomesia agavoides Castañeda should be placed in the genus Ariocarpus.
Anderson, Edward F. (Whitman Coll., Walla Walla, Wash.) A revision of Ariocarpus (Cactaceae). III. Formal taxonomy of the subgenus Roseocactus. Amer. Jour. Bot. 50(7): 724–732. Illus. 1963.—This is the first of 2 articles dealing with the formal taxonomy of Ariocarpus. The introduction contains sections on geographical distribution and habitat, policy of classification, and herbaria consulted. Acknowledgments are made to those who assisted in research or field studies. A description of the genus and a key to the subgenera and species is followed by a formal taxonomic treatment of the subgenus Roseocactus. This treatment includes a description, illustrations, a map of authenticated collection sites, citation of common names, a discussion of synonomy and types, and a list of specimens examined of each species and variety. The accepted species which are discussed are Ariocarpus kotschoubeyanus and A. fissuratus. The latter species consists of 2 varieties, var. fissuratus and var. lloydii.
The four species considered in this article fall into two natural groups. The evidence presented for this conclusion involves not only external features such as floral, fruit, and seed morphology, but also that obtained from internal structure, including tubercle and areole development, the anatomy of surface layers of mature tubercles, the structure of crystals in the ground tissues, and features of tracheary elements. When all evidence is considered, it becomes apparent that Pelecyphora aselliformis and Encephalocarpus strobiliformis are cogeneric as are P. valdeziana and P. pseudopectinata. Yet, the two cogeneric pairs are not closely related to each other. We do not propose to place them in any phylogenetic scheme as yet because general knowledge of the family Cactaceae is still too fragmentary. The first pair is assigned to Pelecyphora, of which a formal taxonomic treatment is presented, and the second pair is tentatively assigned to Thelocaclus.
Structural and developmental data indicate that Lophophora (Cactaceae) should be retained as a genus, which appears to be most closely related to Thelocactus (sensu lato). Within Lophophora morphological differences suggest that two species should be recognized. In the extensive northern population (Texas along the Río Grande to San Luis Potosí in Mexico) the tubercles are usually arranged as distinct ribs or elevated podaria, whereas in the restricted southern population (limited to the Mexican State of Querétaro) podaria and ribs are poorly developed or lacking and there are also differences in pollen structure. We believe that these two populations should be recognized as distinct species, L. williamsii and L. diffusa, respectively. We further believe that the latter represents the ancestral type.
This is the second of 2 articles (Nos. III and IV) dealing with the formal taxonomy of Ariocarpus. A description of the genus and a key to the subgenera and species appeared in the third article of the series. This article includes a description, illustrations, a map of authenticated collection sites, citation of common names, a discussion of synonymy and types, and a list of specimens examined of each species in the subgenus Ariocarpus. The accepted species which are discussed are Ariocarpus retusus, A. agavoides, A. trigonus, and A. scapharostrus.
The monotypic genus Obregonia Frič was compared with Ariocarpus, Lophophora, Strombocactus, and certain other cactus genera. Obregonia and Ariocarpus are similar in characters of seeds, seedlings, habitat, fruits, and general habit. They differ in time of flowering, point of flower origin, areole structure, presence or absence of druses and a mucilage system, and presence or absence of spines. Obregonia and Lophophora are similar in characters of seeds, habitat, basic areole structure, and fruits. They differ in seedling form, habit of adult plants, presence or absence of spines, and chemical analysis. Strombocactus resembles Obregonia in few ways except in basic areole structure and some aspects of anatomy. The author concludes that Obregonia is an intermediate form between Ariocarpus and Lophophora and deserves generic rank. A formal taxonomic treatment of the genus follows the conclusions.
Anderson, Edward F. (Claremont Graduate School, Claremont, California.) A revision of Ariocarpus (Cactaceae). I. The status of the proposed genus Roseocactus. Amer. Jour. Bot. 47(7) : 582–589. Illus. 1960.—The proposed genus Roseocactus Berger is found to be a subgenus of Ariocarpus. The subgenera Ariocarpus and Roseocactus are basically similar in habitat, seedlings, presence of mucilage systems, tubercle structure, seed structure, fruiting habit, flower origin and structure, alkaloidal properties, trichomes, pollen grains, and chromosome number. They differ in flower color, presence or absence of an areolar groove, tubercle divergence, and trichome texture. A hypothesis is proposed to explain variations in the areoles. The differences in structure of mature tubercles are thought to be due to variability in the location of growth and elongation with respect to the floral and spinous areolar areas.
Boke, Norman H. (U. Oklahoma, Norman.) Anatomy and development in Solisia. Amer. Jour. Bot. 47(1): 59—65. Illus. 1960.–The genus Solisia contains a single species of small cacti which resemble certain mammillarias in having: pink, lateral flowers; milky juice; and dimorphic areoles. Adult specimens have elongate spiniferous areoles with an unusual sequence of spine initiation. The first four or five primordia appear at the posterior end of the areole meristem; the next are initiated near its center, after which initiation proceeds both acropetally and basipetally until the single, elliptical series of primordia is complete. A similar pattern of spine initiation occurs in Pelecyphora aselliformis, but this species differs markedly from S. pectinata in other respects. In seedlings of S. pectinata the areoles are broadly elliptical and spine initiation is strictly acropetal, a situation found in certain species of Mammillaria. Seeds of S. pectinata are black with a large hilum and a small perisperm. Since the perisperm has apparently been overlooked, it appears that only the black seed coat and relatively large hilum keep the species out of Mammillaria. If Buxbaum's postulates concerning the value of seed structure in tracing phylogeny in the Cactaceae are valid, S. pectinata must have diverged from the main line of evolution somewhere below Neobesseya. In that event, the species probably merits generic rank; otherwise, it seems preferable to return it to Mammillaria.
Boke, Norman H. (U. Oklahoma, Norman.) Endomorphic and ectomorphic characters in Pelecyphora and Encephalocarpus. Amer. Jour. Bot. 46(3) : 197-209. Illus. 1959.—Outstanding ectomorphic characters of Pelecyphora valdeziana include its small size; pectinate, hairy spines; broad, truncate, floral buds; dehiscent, berry-like fruits; and black, tuberculate seeds. The leaves are vestigial, and although the areole meristem originates on the adaxial face of the tubercle primordium, it is soon elevated to the summit by intercalary growth. The first primordium of the single, elliptical series of spines is initiated immediately in front of the rudimentary leaf. Others form in acropetal sequence on either side of the areole meristem. The last ones form across the areole, leaving a meristem, which may be floral or vegetative, on the anterior side. Whether areoles of P. valdeziana can be considered dimorphic is doubtful. However, they approach the type of dimorphism found in Epithelantha. Pelecyphora aselliformis has acuminate floral buds; dry, papery fruits; and brown, curved, reticulate seeds. The leaves are reduced almost to extinction. The areole meristem becomes separated into spiniferous and axial portions early in ontogeny, but the 2 parts remain connected by a band of trichomes, which probably represents a vestigial groove. The axial meristem may be reproductive or vegetative. The sequence of spine initiation in P. aselliformis is unusual in that it begins at the anterior side of the spiniferous meristem and proceeds toward the posterior side. Areoles in this species are clearly dimorphic, much as in the mammillarias, but the vestigial groove is reminiscent of Coryphantha and related genera. Although adult specimens of Encephalocarpus strobiliformis bear scale-like tubercles, which are very different from the laterally compressed tubercles of P. aselliformis, their flowers, fruits, and seeds are almost identical. The two species share the same type of areole dimorphism, including the vestigial groove. Tubercles on seedlings and young branches of E. strobiliformis are prismatic rather than scale-like. Since they tend to be laterally compressed at the summit and bear elliptical areoles with many more spines than the adult, they resemble seedling tubercles of P. aselliformis. Tubercles on adult specimens likewise resemble each other in the structure of the epidermis and hypodermis. It does not seem possible that P. valdeziana can be retained in the genus Pelecyphora. If seed structure has any systematic value, the species belongs in or near the genus Thelocactus, to which it was assigned by Bravo. Pelecyphora aselliformis and Encephalocarpus strobiliformis, on the other hand, share so many important characters that they could well be considered cogeneric. Both seed structure and the rudimentary grooves on the tubercles suggest that their affinities may lie with certain coryphanthas or mammillarias rather than with Ariocarpus and Epithelantha.
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