THE ALLIUM INFLORESCENCE: SOME SPECIES OF THE SECTION MOLIUM

MANN, Louis K. (U. California, Davis.) The Allium inflorescence: some species of the section Molium. Amer. Jour. Bot. 46 (10): 730-739. Illus. 1959.-The inflorescence is described for Allium neapolitanum, A. roseum, A. hirsutum, A. subhirsutum, A. zebdanense and A. erdelii, species of Molium, a Mediterranean section of the genus. Inflorescence structure is similar among these 6 species. The single spathe appears to consist of 4 coalesced bracts, each of which bears in its axil a bostryx (helicoid cyme) of 3-7 flowers. Central to these 4 peripheral bostryxes are several smaller ones which differentiate later and decrease in flower number toward the inflorescence center. Bracts and bracteoles (prophylls) are generally absent within the spathe. The inflorescence is not radially symmetrical and the bostryx on the side opposite the uppermost foliage leaf differentiates and develops first. Among the peripheral bostryxes there is a definite sequence of development and certain regularities of coiling (clockwise vs. counterclockwise). Within each bostryx the flowers open in a strict sequence from oldest to youngest; among the bostryxes, the 4 peripheral ones flower first, usually starting with the first bostryx to be differentiated. The central bostryxes flower last. THE GENUS Alliumn, with its some 500 species, is a morphologically diverse group. As in many large genera, certain species show obvious similarities, and these may, with considerable convenience, be placed under sub-generic names. George Don (1827), the first post-Linnean monographer of Allium, divided the genus into a number of such groups, most of which are still used today, at least in name. Others have been added, and Stearn (1946a), in an excellent review of the old-world alliums, has given the history of these sections and perhaps the best summary we have of their current status (see also Stearn, 1946b, 1946c). Feinbrun (1954) has pointed out the relationships among chromosome numbers, chromosome morphology, and certain anatomical characteristics within the sections. Although many of the sections are probably natural groupings (e.g., Codonoprasum) and have been clearly and consistently used since first proposed by Don, others are not (e.g., Rhizirideum), and have been constant sources of confusion. Most of the sections are based on a single character e.g., Alliotypus is characterized mainly, by the long lateral cusps of the inner stamens, and Rhizirideum by a well-developed rhizome. For a clear understanding of the limits and relationships of the sections, much more morphological and cytological information must be developed. Inflorescence structure appears to be extremely varied within Aillium, and while available data are too few and conflicting to be used in describing or 1 Received for publication May 4, 1959. This paper was begun while the author was a John Simon Guggenheim Fellow at the Royal Botanic Gardens, Kew. Work has continued under National Science Foundation grant G-3940. The author appreciates the kindness of the Director, the Royal Botanic Gardens, Kew, and of many members of the staff, particularly Dr. C. R. Metcalfe, Keeper of the Jodrell Laboratory, where the author worked. delimiting the sections, this approach appears to be a promising one. In the present paper, the inflorescence is described for several species of the section Molium, a moderately well-defined Mediterranean and east Mediterranean section of perhaps 20-25