POLYPLOIDY IN SOUTH AFRICAN SPECIES OF ALOË

RILEY, HERBERT PARKES (U. Ke ttucky, Lexington.) Polyploidy in South African species oi Aloe. Amer. Jour. Bot. 46(2): 126-119. 1959.-Chromosomes were studied from 167 plants of 40 species of Aloi and from 1 unidentified plant; these include 40 plants of A. Davyana growing wild in the Transvaal. In all but 2 plants the diploid complement consisted of 8 long and 6 short chromosomes. The 2 plants of A. ciliaris -which were studied were hexaploid with 42 somatic chromosomes. Chromosome counts include 12 species of Aloi from which chromosome numbers apparently had not been determined previously. MOST MEMBERS of the tribe Aloineae of the Liliaceae are characterized by a haploid chromosome complement that consists of 4 long and 3 rather small chromosomes. This pattern is reflected in most of the plants of A1oe, Gasteria, Haworthia and Astroloba (Apicra) that have been studied cytologically, but a small percentage of the plants of each of these genera are polyploids and a fairly large number of polyploids are found in the Coarctatae and Tessellatae sections of Haworthia. Apparently the first chromosome study on this tribe was made in 1912 by H. A. C. Muller who found that the 2n number was 14 in A1oe striata Haw. which he reported under the name of A. Hanburyana Naud. Some years later Taylor (1925) made a comparative study of the chromosome morphology of A1oe, Gasteria and Haworthia, emphasizing especially the number and location of satellites in the 3 genera and suggesting that "a grouping of the species based on chromosome characters would in general correspond-to that adopted by the systematist." His conclusions on the taxonomic possibilities of these satellites were questioned by Resende (1937) who found no constancy in their number and position within any of the taxa. Apparently the first polyploid to be found was A. ciliaris which was reported by Resende in 1938. A number of investigators have studied the chromosomes of A1oe. The more extensive studies, i.e., 1Received for publication August 18, 1958. 2This paper represents a joint contribution from the Department of Genetics of the University of Pretoria and the Department of Botany of the University of Kentucky. Much of the work was carried out while the author was a Fulbright lecturer in South Africa and it was aided in part by grants from the Joseph Henry Fund of the National Academy of Sciences and the Research Fund of the University of Kentucky. The writer is indebted to Dean M. M. White of the College of Arts and Sciences of the University of Kentucky for a leave of absence, to Professor J. D. J. Hofmeyr for permission to work in his department at Pretoria, to Mr. A. Berg of Pretoria, Mr. H. Hall of Cape Town and Dr. E. A. Schelpe of Cape Town for plants and seeds, to Mrs. Eily Gledhill, Dr. A. R. H. Martin and Mr. A. R. A. Noel of Rhodes University and Mrs. M. R. Levyns of the University of Cape Town for guiding him to aloes in the field and to Professor F. G. Schweicherdt of the tJniversity of Pretoria for his last available copy of Miiller's dissertation on Aloe. those in which more than 3 species or hybrids were examined, were made by Ferguson (1926), Fernandes (1930, 1931), Kondo and Megata (1943), Muller (1945), Resende (1937), Sato (1937, 1942) and Snoa (1951). A survey of the literature (Darlington and Wylie, 1955; Delay 1950; et al.) reveals that approximately 95 identified South African species have counts reported for them; only 2, A. ciliaris Haw. and A. tenuifolia Lam., are known to be wholly polyploid, while A. Tidmarshii (Schonl.) F. S. Muller (= A. ciliaris var. Tidmarshii Schonl.) includes some plants with 14 and some with 42 chromosomes. Of 14 described varieties of these South African species, only A. ciliaris f. gigas Res. (= A. gigas Res.), a plant found only in the Coimbra Botanical Garden in Portugal, is reported as having more than 14 diploid chromosomes. A 2n number of 14 has been reported in 2 horticultural forms (Resende, 1937; Snoad, 1951) and 21 putative hybrids (Fernandes, 1930, 1931; Gioelli, 1930; Resende, 1937; Sato, 1937, 1942; Kondo and Megata, 1943; Afify, 1945; Muller, 1945; Mendes, 1950 and Snoad, 1951), some of which have been listed as species. Thirty-five unidentified plants were examined by Resende (1937), Mendes (1950) and Snoad (1951), and all were diploids except 1 pentaploid and 4 hexaploid plants growing at the John Innes Horticultural Institution. Although a study of polyploidy in any given taxon may be interesting in its own right, it becomes doubly so in the Aloineae in connection with Kostoff's (1939) and Darlington's (1956) ideas about polyploidy. Darlington (pages 103-104) states that in long-lived plants the chromosome number changes less than in short-lived plants and that the stability of chromosome numbers is correlated with the length of the reproductive cycle. He was probably thinking primarily of trees and shrubs in this connection, but it must be remembered that the Aloineae, even the non-tree-like forms, probably live as long as some "woody plants." If such succulents are considered to be long-lived plants they, should exhibit little, if any, variation from the diploid number. As shown from the literature, the aloes agree with this thesis as they have a rather low percentage of polyploids.