Annals of botany · 2026
Comparative floral morphoanatomy and the progamic phase reveal conserved reproductive organization in Pilostyles (Apodanthaceae).
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Ortega-González Pactli F, Vázquez-Santana Sonia
Аннотация
BACKGROUND AND AIMS: Contrasting reproductive systems can be associated with differences in floral structure and reproductive function. In the endoparasitic genus Pilostyles (Apodanthaceae), reproductive systems range from unisexual chasmogamous to hermaphroditic cleistogamous flowers. However, it remains unclear whether these systems differences are associated with floral organization and the pollen-tube pathway. We compared floral morphoanatomy and pollen-tube development in the three Mexican species of Pilostyles to characterize similarities and differences in floral organization and reproductive function.
METHODS: Floral anatomy was examined using light, confocal, and scanning electron microscopy, together with histochemical analyses, to characterize the pollen-tube pathway during the progamic phase in Pilostyles maya, P. mexicana, and P. thurberi.
KEY RESULTS: Despite their contrasting reproductive systems, the three species shared a largely conserved floral organization, including a perigonium, central reproductive column, transmitting tissue, unilocular ovary, parietal placentation, schizogenous funiculus, and anatropous bitegmic ovules. The pollen-tube pathway was also largely conserved, with pollen tubes growing from the stigma through the transmitting tissue to the ovules via the micropyle. In the cleistogamous flowers of P. maya, pollen tubes followed an additional route, germinating within dehiscent pollen sacs and growing directly into the transmitting tissue through the stigma, consistent with autonomous within-flower selfing. Histochemical analyses confirmed activity in androecial secretory cells and nectary disks of P. mexicana and P. thurberi, whereas no secretory activity was detected in the nectary disk of P. maya.
CONCLUSIONS: The three Pilostyles species reveal contrasting reproductive systems that were associated with little apparent modification of floral organization or pollen-tube guidance. Despite differences in reproductive traits, the species share a largely conserved structural framework for flower function. This study provides the first comprehensive characterization of the pollen-tube pathway during the progamic phase in Pilostyles and new insights into reproductive diversity and function in endoparasitic angiosperms.
METHODS: Floral anatomy was examined using light, confocal, and scanning electron microscopy, together with histochemical analyses, to characterize the pollen-tube pathway during the progamic phase in Pilostyles maya, P. mexicana, and P. thurberi.
KEY RESULTS: Despite their contrasting reproductive systems, the three species shared a largely conserved floral organization, including a perigonium, central reproductive column, transmitting tissue, unilocular ovary, parietal placentation, schizogenous funiculus, and anatropous bitegmic ovules. The pollen-tube pathway was also largely conserved, with pollen tubes growing from the stigma through the transmitting tissue to the ovules via the micropyle. In the cleistogamous flowers of P. maya, pollen tubes followed an additional route, germinating within dehiscent pollen sacs and growing directly into the transmitting tissue through the stigma, consistent with autonomous within-flower selfing. Histochemical analyses confirmed activity in androecial secretory cells and nectary disks of P. mexicana and P. thurberi, whereas no secretory activity was detected in the nectary disk of P. maya.
CONCLUSIONS: The three Pilostyles species reveal contrasting reproductive systems that were associated with little apparent modification of floral organization or pollen-tube guidance. Despite differences in reproductive traits, the species share a largely conserved structural framework for flower function. This study provides the first comprehensive characterization of the pollen-tube pathway during the progamic phase in Pilostyles and new insights into reproductive diversity and function in endoparasitic angiosperms.