Two sexes and many colours of Cylindropuntia wolfii

Fertility hidden in flower structure

Cylindropuntia wolfii (formerly Opuntia wolfii) is functionally dioecious. Individual plants supply pollen or produce seeds after pollination. Flowers retain structures of both reproductive systems, but anthers of female flowers are sterile, and female function is reduced in male flowers. Identifying the sexual system therefore requires assessing organ fertility. [Ramadoss et al. 2023]

Colour and size as signal traits

Six flower colour classes were observed in the Mountain Springs population, from green through yellow and orange to red. Male flowers were larger and paler on average, and more often greenish-yellow. Female flowers more often fell in the orange-red part of the variation. The overlapping ranges mean that sex and colour remain two related but separately described traits. [Ramadoss et al. 2023]

In observations of 75 plants, male flowers received more insect visits. Size and colour measurements were made within the same study, but their effects were analysed separately. The result shows covariation of traits and visits. Strict separation of colour and size effects would require independent manipulation of these properties. [Ramadoss et al. 2023]

What fluorescence reveals

Anthers of female flowers showed stronger green fluorescence. Signal location corresponded to regions of anther tissue changes, including the tapetum, a layer involved in pollen development. The authors considered whether such a signal might maintain insect interest in flowers without fertile pollen. This is a hypothesis of ecological function based on optical measurements and anatomy. [Ramadoss et al. 2023]

Transport between flowers was tracked with fluorescent powder replacing pollen. The marker was detected in only some flowers studied. The trial describes material movement over a defined period, complementing visit counts, which alone also include contacts without successful pollination. [Ramadoss et al. 2023]

History recorded in genotypes

The 2025 analysis covered six cholla species with different reproductive systems. In hexaploid C. wolfii, most adult samples were genetically distinct, although repeated clones were also found. At the same time, propagules from broken segments were observed in field plots, and identified seedlings were absent. Adult plant variation thus retains evidence of earlier sexual recruitment, while the current picture indicates a large vegetative role. [Ramadoss et al. 2025]

The authors consider a shift towards clonality, but the data also allow rare, episodic seedling emergence. One population represented each of the six species, differing from the others in features including ploidy and history. Dioecy is one component of this biology, alongside partner numbers, pollen transfer effectiveness and conditions for young plant survival. [Ramadoss et al. 2025]