Sex identified through function
Functional dioecy divides plants in a population into individuals that donate pollen and individuals that produce seeds. The external structure of the flowers can retain components of both roles. In New Mexican populations of Echinocereus coccineus, Hoffman combined anther appearance with controlled pollination and subsequent fruiting. Plants with well developed anthers produced pollen, while fruits formed on plants with reduced anthers. Appearance was thus linked to actual reproductive function. [Hoffman 1992]
Further explanation came from Hernández-Cruz and colleagues in 2018. One population of each of five taxa was examined. Four represented a dioecious system, while bisexual Echinocereus triglochidiatus provided a comparison. Comparison with a close relative helped identify the stage at which male or female flower development diverges from the course leading to both functions. [Hernández-Cruz et al. 2018]
The layer supporting future pollen
A young anther contains cells whose divisions will give rise to pollen grains. Among the layers surrounding them is the tapetum, which helps nourish developing pollen. Its cells subsequently undergo orderly degradation. In the male and bisexual flowers examined, this process occurred at a stage consistent with normal pollen maturation. The timing of the layer’s disappearance was therefore part of the developmental sequence. [Hernández-Cruz et al. 2018]
In female flowers, stamen primordia began to develop, after which the tapetum degraded prematurely. Microspore mother cells died before meiosis, the division producing cells with a reduced chromosome number. Pollen development stopped at that stage. Shriveled, empty anthers remained in the mature flower. Female function was retained because the pollinated pistil could support seed production. [Hernández-Cruz et al. 2018]
A pistil functional through fertilisation
Male flowers retained developed stigmas, styles and ovules. Following pollination, pollen grains germinated on the stigma. Their pollen tubes grew through the style, reached the ovary and entered the ovules. Zygotes, the cells formed following fertilisation of egg cells, were also observed. This sequence places the loss of female function later than pollen reception itself. [Hernández-Cruz et al. 2018]
The initially developing seeds of male flowers then failed to mature. Changes involved tissues associated with their supply, including the funiculi connecting ovules to the ovary wall and the nucellus. Seeds and fruits collapsed. In female flowers, fertilisation was instead followed by the formation of fleshy fruits, whitish pulp and mature black seeds. Similarity at flower opening thus concealed a difference that became apparent over the following days. [Hernández-Cruz et al. 2018]
How cell death was investigated
The researchers combined histological sections, electron microscopy and TUNEL assays. The assay labels free DNA ends generated during fragmentation. Together with the appearance of degenerating tissues, it provided evidence of involvement of programmed cell death. Signals appeared early in the tapetum and future pollen cells of female flowers and during arrested seed development in male flowers. Controls were also used to assess labelling specificity. [Hernández-Cruz et al. 2018]
Some cells also undergo this process during normal flower and seed development. The significance of a result therefore depends on its location and timing. The authors proposed heterochrony, a change in the timing of developmental events, as an explanation for male sterility in female flowers. Earlier tapetum degradation interrupts a sequence that leads to mature pollen in male flowers. Identification of the genes regulating this process remained a task for further research. [Hernández-Cruz et al. 2018]
Names and experimental scope
The shared developmental pattern was described in the studied Echinocereus coccineus, Echinocereus polyacanthus, Echinocereus pacificus and the taxon presented in the paper as Echinocereus mombergerianus. POWO now treats the last name as a synonym of Echinocereus pacificus subsp. mombergerianus. Retaining this connection links the findings to the correct plants despite the change in taxonomic rank. [Hernández-Cruz et al. 2018] [2-WWW]
The experiment concerns particular populations, which define the demonstrated scope of the mechanism. The comparison shows how two different timings of reproductive loss lead to a division of roles between individuals. Anther appearance, pollen presence, the outcome of controlled pollination and subsequent fruit development are all informative when observing plants. Each stage provides different information about floral function. [Hernández-Cruz et al. 2018] [Hoffman 1992]
Functional Dioecy in Echinocereus: Ontogenetic Patterns, Programmed Cell Death, and Evolutionary Significance
Hernández-Cruz R., Barrón-Pacheco F., Sánchez D., Arias S., Vázquez-Santana S., Functional Dioecy in Echinocereus: Ontogenetic Patterns, Programmed Cell Death, and Evolutionary Significance, International Journal of Plant Sciences, 2018, 179(4):257-274, doi: 10.1086/697072
A comparative study of flower and seed development in five Echinocereus taxa. Controlled pollination, histology, electron microscopy and TUNEL assays revealed different timing of the loss of male and female function in the studied dioecious taxa. The authors discuss the association of sterility with programmed cell death and propose a heterochronic interpretation.
Functional dioecy in Echinocereus coccineus (Cactaceae): breeding system, sex ratios, and geographic range of floral dimorphism
Hoffman M. T., Functional dioecy in Echinocereus coccineus (Cactaceae): breeding system, sex ratios, and geographic range of floral dimorphism, American Journal of Botany, 1992, 79(12):1382-1388, doi: 10.1002/j.1537-2197.1992.tb13748.x
Field research and controlled pollination in New Mexico demonstrated functional dioecy in the studied Echinocereus coccineus populations. The paper describes differences between male and female flowers, sex ratios, bee visitation and geographic variation in floral dimorphism under the historical circumscription of the species.
Plants of the World Online — Royal Botanic Gardens, Kew
Accepted names, synonyms and distribution. A citation beside a taxon leads to its record.
Accessed 2026-10-08.