A Contribution to Cytology in Cornales

Abstract

Chromosome counts in Nyssa and Camptotheca indicate a base number of x = 22 for Nyssaceae. Davidia, the only genus of Davidiaceae, has x = 21. In Cornaceae, where x = 11 was thought basic, Mastixia has n = 13 and 11, while Curtisia, recently excluded from Cornaceae as Curtisiaceae, has n = 13. Nyssaceae and Davidiaceae appear more closely related to Cornaceae than previously recognized subfamilies and tribes of this family, and segregation of Helwingia, Mastixia and Curtisia from Cornaceae as proposed by other workers is supported on cytological grounds. While preparing a review of angiosperm cytology in relation to phylogeny, Raven (1975) was able to point out important gaps in the chromosome record for flowering plants. One of the groups where information was conspicuously lacking was the Cornaceae and its allied families Nyssaceae, Davidiaceae, and segregates such as Curtisiaceae. An attempt was made to learn more of the cytology of these families, and by the time the review went to press (Raven, 1975), chromosome numbers had been determined for several rare and taxonomically critical genera. Most of these counts were available in time for inclusion in the review, but were not fully documented there. This paper, therefore, presents in detail the results of this recent chromosomal study with a short discussion of the possible significance to the systematics of the families concerned. The counts were made mainly by the writer but also by L. Riidenberg and W. Tai, and with their permission, are also reported here. MATERIALS, METHODS, AND OBSERVATIONS Meiotic studies were made of most of the species investigated. Buds were fixed in Carnoy's solution (ethanol-acetic acid, 3:1) and stored in 70% ethanol. 1Thanks are extended to the following for their assistance in providing materials used in this study: D. E. Breedlove, California Academy of Sciences, for buds of Davidia involucrata from plants at the Strybing Arboretum; Setijati Sastrapadja, Director, National Biological Institute, Bogor, Indonesia, for buds of Mastixia trichotoma; K. M. Matthew, St. Joseph's College, Tiruchirapalli, India, for buds of M. arborea; B. Bartholomew, University of California Botanic Garden, for seeds of Cornus capitata; and R. H. Eyde, Smithsonian Institution, for Nyssa sylvatica var. sylvatica and for arranging the collection of buds of N. ogeche by R. K. Godfrey, Florida State University, and N. sylvatica var. biflora by J. Stubbs, U.S. Forest Service. Counts for Mastixia trichotoma were made by W. Tai, Department of Botany and Plant Pathology, Michigan State University, while Lily Rudenberg, Gray Herbarium, Harvard University, counted one of the collections of Davidia involucrata studied here. The author is recipient of grant DEB-76-19907 from ;the U.S. National Science Foundation. Collection of Mastixia arborea was made possible by a travel grant to Dr. Eyde from the Smithsonian Institution's Foreign Currency Program. 2 B. A. Krukoff Curator of African Botany, Missouri Botanical Garden, 2345 Tower Grove Avenue, St. Louis, Missouri 63110, U.S.A. ANN. MissouRI BOT. GARD. 65: 650-655. 1978. 0026-6493/78/0650-0655/$00.75/0 This content downloaded from 157.55.39.58 on Thu, 25 Aug 2016 05:04:00 UTC All use subject to http://about.jstor.org/terms 1978] GOLDBLATT-CYTOLOGY IN CORNALES 651 Mitotic studies were made in the case of Mastixia trichotoma, where a count was obtained from tapetal cells of developing anthers, and from root tips in Camptotheca, Cornus capitata and Curtisia. Camptotheca cuttings were supplied by the U.S. Department of Agriculture Plant Introduction Station, Chico, California, and grown at the Missouri Botanical Garden. Curtisia and Cornus capitata were grown from seed collected in the wild and also grown at the Missouri Botanical Garden. Root tips were pretreated in 0.003 M hydroxyquinoline for five hours at refrigerator temperature. After fixation they were hydrolyzed in 10% HCI and stained in lactopropionic orcein (Goldblatt, 1976). Chromosome counts obtained in the study are listed in Table 1, where collection data and voucher information is also given.