Systematics Section / ASPT
Baker, Marc A. .
Morphological and cytological analyses in Cylindropuntia (Cactaceae): the circumscription of C. multigeniculata, C. echinocarpa, and C. whipplei; including the resurrection of C. whipplei var. enodis.
A morphological and cytological study was conducted to elucidate taxonomic relationships among Cylindropuntia echinocarpa, C. multigeniculata, and C. whipplei, with C. bigelovii initially used as an outgroup. Chromosome determinations from all populations were diploid (2x =22) except for those of C. whipplei var. enodis and one population of C. whipplei var. whipplei, which were tetraploid (4x = 44); and one population of C. bigelovii, which was triploid (3x = 33). Mean pollen stainability for C. multigeniculata was 86.5%. Morphological analysis included iterations of multivariate techniques, including Principle components analysis (PCA), discriminant function analysis (DFA), multivariate analysis of variance (MANOVA), and unweighted pair group method with arithmetic mean (UPGMA). Twenty two continuous characters were measured for 761 individuals representing 24 populations. Results indicated two morphological clines beginning with the eastern diploid form of C. whipplei. The cline north of the Grand Canyon remained diploid, becoming spinier and more densely-branched to the drier regions of the west and morphologically distinct as C. multigeniculata. The southern cline, which is represented by tetraploid populations of C. whipplei, also migrated west into drier regions but south of the Grand Canyon; became diminutive in terms of habit, stem diameter, and spine number; and morphologically distinct as C. whipplei var. enodis. The easternmost tetraploid population, however, which is the type locality for C. hualpaensis, is both geographically and morphologically closer to typical C. whipplei. UPGMA indicated that populations of C. echinocarpa were the most morphologically distinct compared to those of all other taxa. Cylindropuntia echinocarpa, which is non-clonal, probably represents a better choice as an outgroup than C. bigelovii, which primarily apomictic.
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1 - Arizona State University, School of Life Sciences, Asu, Main Campus, Po Box 874501, Tempe, Arizona, 85287-4501, USA
Presentation Type: Oral Paper
Date: Monday, August 15th, 2005
Time: 2:00 PM