Cytotaxonomy of the Andropogoneae 1. Subtribes Dimeriinae and Saccharinae
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272 Cytologia 21 Cytotaxonomy of the Andropogoneae 1. Subtribes Dimeriinae and Saccharinae Robert P. Celarier Department of Botany and Plant Pathology, Oklahoma A. and M. College, Stillwater, Oklahoma, U. S. A. Received May 2, 1956 The grass tribe Andropogoneae is considered by many workers (Hartley, 1950, Bews, 1929) to be the most highly specialized of the grasses, and few would disagree with this if the small related group, the Maydeae, were included. The tribe is characteristically tropical and subtropical, although many species of a few genera are found in the temperate regions. The maximum abundance of genera and species is seen in southeast Asia, principally in the Indo-Malaya area (Hartley, 1950). Bews (1929) has proposed that the more advanced grasses are to be found in the drier regions of subtropical grass lands, and the Andropogoneae are very abundant and often dominant in tropical savannahs. The available morphological and geographical information suggests that the tribe is of comparatively recent origin; that it probably originated in the tropical forests of the Indo-Malaya area, and radiated from there to the tro pical savannahs. A few members have advanced into the temperate regions of North America and Eurasia. It is further suggested (Hartley, 1950) that they have not yet reached their full potential in the temperate areas, especial ly in the Western Hemisphere. From these facts one might expect the group to be in an active state of evolution in which many types and all stages of reproductive isolation would be represented. The morphological evidence, as seen in the numerous tax onomic controversies at both generic and specific levels, suggests that in many cases the isolation is not yet complete. In spite of the apparent attractiveness of the group for studies of ex perimental evolution only a few have been made (Mangelsdorf and Reeves, 1939; Reeves and Mangelsdorf, 1942; Randolph, 1955; Garber, 1944, 1950a, 1950b, 1954; Gould, 1953). There is little information on the chromosome cytology of the group and it is the objective of this report to add addi tional cytological information, and to bring together the scattered literature. This review includes the Maydeae although it is considered to be a separate tribe by many workers. It appears to the author that the Maydeae are a natural extension, through specialization, of the Androgoneae and from the standpoint of experimental taxonomy it seems desirable to study them together. 1956 Cytotaxonomy of the Andropogoneae . I 273 Although most taxonomists are in agreement concerning the constitution of the tribe, there is much disagreement regarding the number of genera and species to be included. Hackel (1889), in the first thorough treatment of the tribe, recognized only a relatively few valid genera . In general his system was followed (Hooker, 1897; Trimen, 1900) until the work of Stapf (1919) on the grasses of tropical Africa. Stapf disagreed with Hackel principally in breaking up the latter's genus Andropogon into a number of small genera and in establishing numerous subdivisions. He also added a large number of previously undescribed tropical species. Since Stapf's work most taxonomists working in the tropics, where the tribe is most abundant have, in general , accepted his treatment (Camus and Camus, 1922; Hubbard, 1934; Blatter and McCann , 1935; Keng, 1939; Henrard, 1940; Bor, 1940; Rhind, 1945). On the other hand most tax onomists in the temperate regions have either accepted Hackel's treatment or more frequently a modification of it (Komarov, 1934-45; Hitchcock, 1950; Hegi, 1936; Post, 1933). This is somewhat to be expected since the tem perate zones have so few members of the tribe represented that there is little problem of identification; however, quite the opposite is true in the tropics. The division of the Andropogoneae into subtribes has been treated by many workers (Stapf, 1919; Bews, 1929; Keng, 1939; Pilger, 1940; 1954) since the original work of Hackel (1889). The number of subtribes propos ed varies from four (Bews, 1929) to eight (Keng, 1939), but the must recent treatment (Pilger, 1940; 1954) is somewhat intermediate and includes six. In the present report the proposal of Pilger is followed with occasionally further breakdowns within subtribes for convenience of grouping, and the Maydeae are included. These categories are usually easily separated with the following key: I. Spikelets perfect, or with staminate, neuter and perfect spikelets mixed in same inflorescence. 1. Spikelets borne singly on axis of the simple raceme and laterally compressed. DIMERIINAE 2. Spikelets borne in pairs on axis of the simple raceme (occasionally the pedicel late spikelet suppressed) and dorsally compressed. A. Joints and pedicels slender, not fused. (1) Spikelets all alike. SACCHARINAE (2) Spikelets of pairs differing in sex. (a) Inflorescence an open panicle, joints and pedicels not grooved SORGINAE (aa) Racemes digitate, binate, or solitary, not a panicle (Capillipe dium has an open panicle but the joints and pedicels have a translucent groove) ANDROPOGONINAE AA. Joints and pedicels stout and often fused to form a receptacle for the sessile spikelet. (1) Fertile spikelets 2-flowered and awned ISCHAEMINAE (2) Fertile spikelets 1-2-flowered, awnless ROTTBOELLINAE *19 274 R. P. Celarier Cytologia 21 II. Spikelets unisexual, the staminate and pistillate in different inflorescences, or different parts of same inflorescence. MAYDEAE Materials and methods All materials reported on in this study were grown in an experimental nursery at the Oklahoma Agricultural Experimental Station. The nursery is situated on a rather uniform plot of land and each entry was planted in short rows of 18-20 plants. A number of entries failed to flower under our long day summer conditions and two plants from each of these entries were dug up in the fall, transferred to pots, and taken to the greenhouse. Most of these flowered during the short day, winter conditions. Bud material was taken from all entries, fixed in Carnoys fluid, and stored in the refrigerator until studied. Some entries gave good preparations over a year after fixation. Chromosome studies were made of the meiotic divisions using the standard smear technique and staining in acetocarmine. Herbarium specimens of all entries have been placed in the Oklahoma A. & M. College Herbarium and, in most cases, replicates were deposited in the following herbaria: Royal Botanic Gardens Herbarium, Kew, England; University of Pretoria Herbarium, Pretoria, South Africa; Missouri Botanical Garden Herbarium, St. Louis. Missouri; University of California Herbarium, Berkeley, California, and the U. S. National Herbarium, Washington, D. C. The identity of the critical material has been verified by E. R. Sohns of the U. S. National Museum. SUBTRIBEI. DIMERIINAEC. E. HUBB. This subtribe is represented by only one genus, Dimeria. Although a genus of above average size (ca. 20 species) it is restricted geographically to the Indo-Malaya area, China, and North Australia. However, it appears to have been introduced in a few of the Pacific Islands. There is no cytological information for any of the species. This is much needed in view of its isolation from the rest of the Andropogoneae and its supposed primitive phylogenetic position. SUBTRIBEII. SACCHARINAEKUNTH. The subtribe, as described by Pilger (1940), is divided into two groups. One, the Saccharininae, includes Imperata, Sclerostachya, Miscanthns, Ec coilopus, Eriochrysis, Narenga, Saccharum, Spodiopogon, Erianthus and Miscanthidium, and the other, Eulaliininae, includes Ischnochloa, Micro stegium, Apocopis, Polliniopsis, Eulaliopsis, Homozeugos, Eulalia, Pogona therum, Pseudopogonatherum, Lophopogon, Sclerandrium and Polytrias. All of the members of the Saccharininae are treated together by Bews (1929) and Keng (1939), but in the Eulaliininae there are considerable differences in their treatments. Keng in creating a new subtribe, the Apocopeae, places Apocopis, Eulaliopsis, Homozeugos, Pogonatherum and Lophopogon together 1956 Cytotaxonomy of the Andropogoneae. I. 275 with two other genera Trachypogon and Germainia. Bews also treated many of these as closely related to one another and far removed from the Saccharinae, however, Hubbard (1935) treats them together as Polliniastrae. Of the twenty-two genera listed most are rather small and four (Isch nochloa, Polliniopsis, Eulaliopsis, and Polytrias) are represented by only one species. Only three genera (Erianthus, Microstegiur, and Eulalia) have as many as twenty-five species. Most of the genera are restricted to tropical Asia but two (Homozeugos and Miscanthidium) are found only in Africa and one genus, Eriochrysis, is found in both tropical Africa and tropical America. Key to the genera of the Saccharinae AA. Racemes in more or less compound panicles on an elongated primary floral axis, spikelets one-flowered (two in Spodio pogon), lemma two-lobed with the awn from between the lobes, or awnless. (Saceharininae) A. Axis of the rachis continuous, or disarticulating tardily, spikelets falling free, all spikelets pedicellate. I. Racemes verticillate, lemma deeply lobed .......... Eccoilopus II. Racemes not verticillate, lemma not, or scarcely, lobed. 1. Spikelets awnless. a) Racemes in spike-like panicles, first glume somewhat delicate, stamens one or two ...................... Imperata b) Racemes in open panicles, first glume hardened, stamens three .......... Sclerostachya 2. Panicles abundantly branched, spikelets usu ally awned. a)