Croton californicus Muell. Arg. (Euphorbiaceae) is a subshrub suspected of being dimorphic with phase choices. Gender variation in C. californicus was studied in natural populations of southern California for three years (1994-96) to observe patterns of gender !ability. Some sites exhibited significantly male-biased sex ratios, and these sites often had the greatest number of monoecious morphs, cosexual plants with unisexual flowers. Gender variation was quantified for cosexual plants by calculating the Estimated Floral Gender (EFG) which varied from 1.00 (female) to 0.00 (male). The distribution of the EFG was highly skewed towards maleness. Monoecious individuals were then categorized by their EFG values as phenotypic male, quasi male, equisexual, quasi female, and phenotypic female. Year-to-year gender changes of individual plants were then categorized as inconstancies (changes between one gender category and an adjacent category), phase choices (switches from the male category to female or vice versa), or adjustments (any other changes between non-adjacent categories). Using these categories to distinguish degrees of change, it was possible to show that changes from maleness to femaleness consisted of mostly smaller inconstancies (57%), while changes from femaleness to maleness consisted of larger changes, adjustments (75%) and phase choices (100%). The overall dimorphic gender distribution and the occurrence of phase choices indicates that C. californicus is dimorphic with phase choices, while the directional pattern of gender change towards maleness implies some diphasic qualities. The sexual system of C. californicus may be intermediate between dimorphism with phase choices and diphasy.

This study demonstrates that plants exhibiting phase choices may produce gender changes slowly and/or at low frequencies, making it difficult to observe and identify without large samples studied for several years (three or more). It also suggests that dimorphism with phase choices may be more prevalent than originally thought in plants that exhibit gender dimorphism. Future studies of gender variation in plants could benefit by using this same approach, including comparison, experimentation, and/or genetic analysis.

LLU Discipline





Graduate School

First Advisor

Ronald L. Carter

Second Advisor

Bradford D. Martin

Third Advisor

Gary L. Bradley

Fourth Advisor

Robert A. Cushman

Fifth Advisor

William K. Hayes

Degree Name

Doctor of Philosophy (PhD)

Degree Level


Year Degree Awarded


Date (Title Page)




Library of Congress/MESH Subject Headings

Croton (Plant); Croton Californicus -- Sex differences; Euphorbiaceae -- Sex differences.



Page Count

vi; 55

Digital Format


Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.


Loma Linda University Electronic Theses and Dissertations

Collection Website



Loma Linda University. Del E. Webb Memorial Library. University Archives