Abstract
The number of branches in male and female plants of Cycas micronesica K.D. Hill, Cycas edentata de Laub., Cycas wadei Merr., and Zamia encephalartoides D.W. Stev. were counted in Guam, Philippines, and Colombia, to confirm earlier reports that female plants develop fewer branches than males. Cycas plants produce determinate male strobili and indeterminate female strobili, but Zamia plants produce determinate strobili for both sexes. More than 80% of the female trees for each of the Cycas species were unbranched with a single stem, but more than 80% of the male trees exhibited two or more branches. The mean number of branches on male plants was more than double that of female plants. The number of branches of the Zamia male plants was almost triple that of female plants. Moreover, the Zamia plants produced 2.8-fold greater numbers of branches than the mean of the Cycas plants. Most of Guam’s unsexed C. micronesica trees in 2004 were unbranched, but after 15 years of damage from non-native insect herbivores, most of the remaining live trees in 2020 contained three or more branches. The results confirm that male Cycas and Zamia plants produce more branches than female plants and suggest cycad species with determinate female strobili produce more branches on female plants than species with indeterminate female strobili. Our results indicate that the years of plant mortality on Guam due to non-native insect herbivores have selectively killed more female C. micronesica trees. Horticulture and conservation decisions may be improved with this sexual dimorphism knowledge.
Highlights
Cycads are dioecious gymnosperms that are of horticultural and conservation interest [1,2], and are widely considered the most threatened plant group worldwide [3] primarily due to habitat destruction and the unsustainable trade of wild-collected plants
The unsustainable harvesting of cycads is a major concern at the local level and internationally, where their trade is regulated by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) [4,5]
The unbranched female C. micronesica trees accounted for about 80% of the population
Summary
Cycads are dioecious gymnosperms that are of horticultural and conservation interest [1,2], and are widely considered the most threatened plant group worldwide [3] primarily due to habitat destruction and the unsustainable trade of wild-collected plants. Most short-term field studies of these populations record sex ratio estimates that represent only what was observable at the time of fieldwork. This estimate is variously known as the coning [8], operational [9], or observed sex ratio [10], and it may differ greatly from the true genotypic
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
