INVESTIGATIONS OF NORTH AMERICAN CYCADEOIDS: CONES OF CYCADEOIDEA

KNOBLOCH, IRVING W. (Michigan State U., E. Lansing), and D. M. BRITTON. The chromosome number and possible ancestry of Pellaea wrightiana. Amer. Jour. Bot. 50(1): 52-55. Illus. 1963.Meiotic and somatic chromosome number determinations show that Pellaea wrightiana Hook. is a triploid (2n =87) of hybrid origin. P. ternifolia (Cav.) Link (4x) and P. longimucronata Hook. (2x) (2n = 58) are considered to be the probable parents. PELLAEA WRIGHTIANA was first described by Hooker in 1858 from a New Mexican specimen collected by Charles Wright (No. 2130) in 1851 (see Maxon, 1917). Dr. Alice Tryon (1957), in her monograph on the section Pellaea of the genus Pellaea, refers the taxon to a varietal status under Pellaea ternifolia (Cav.) Link to which it is obviously related in some way. She believes that it is "a northern extension of the species having quantitative differences not sufficient for specific separation." The purpose of the present study is to demonstrate that Pellaea wrightiana is a triploid hybrid, whose probable parents are Pellaea ternifolia (Cav.) Link (4x) and Pellaea longimucronata Hook. (2x). MATERIALS AND METHODs-Specimens from all 3 taxa were collected in various parts of the southwestern United States and northern Mexico. The determinations of chromosome number of Pellaea wrightiana Hook. (Knobloch No. 1624) were made from a plant collected in the Malino Basin of the Santa Catalina Mountains of Arizona. The plants of Pellaea longimucronata Hook. (Knobloch Nos. 1611, 1725) were collected at Texas Canyon and Granite Dells, Arizona. Al' Received for publication, June 17, 1962. 2 Contribution No. 62-2, Botany Department of Michigan State University. though. collections of Pellaea terniJolia (Cay.) Link were made, they were not examined cytologically, since this taxon had been studied by Tryon and Britton (1958) (R. M. and A. F. Tryon Nos. 5105, 5141). Living specimens of both P. wrightiana and P. longimucronata have been grown successfully in the greenhouse and voucher specimens have been deposited in the Michigan State University Herbarium. Meiotic material of P. longimucronata and P. wrightiana was fixed in a 6-3-2 mixture of methanol, chloroform and propionic acid in that order, and then stored in a refrigerator at 5 C. Staining was most successful in Belling's Iron Acetocarmine, and the slides were made permanent by adding a drop of Hoyer's Medium (Beeks, 1955) to the slide before placing the cover slip. The slides were weighted and allowed to dry thoroughly before examining. The somatic chromosome numbers were determined most often on root tips, although crozier leaves were occasionally used. The root tips were pre-treated for 9 hr in a 100-ppm aqueous solution of Actidione. This latter chemical had been successfully used previously (Knobloch, 1953) in shortening long somatic chromosomes. Subsequent steps were the same as for the meiotic material. The photomicrograph and leaf studies were made by Mr. Philip Coleman. The camera lucida drawings were constructed by both of us. This content downloaded from 207.46.13.15 on Sat, 23 Apr 2016 06:16:10 UTC All use subject to http://about.jstor.org/terms