Gynostegium and pollinarium
The gynostegium forms from joined stamen structures and the apical part of the gynoecium. Five units associated with pollination lie around its perimeter. Each pollinarium contains two pollinia, compact pollen packages connected by arms to a central attachment body called the corpusculum. Parts of the attachment apparatus form as a secretion of the apical gynoecium. [Meve and Liede 1994]
Guide rails lie between adjacent anthers. Part of an insect's mouthparts moving upwards along them enters the corpusculum slit. As the fly withdraws its mouthparts, it may remove the entire pollinarium. During the next visit, the transparent edge of a pollinium is deposited in a guide rail. From there, pollen tubes gain access to the relevant gynoecial tissues. [Meve and Liede 1994]
The corona guides the insect's head
The corona forms lobes and projections around the flower centre. In Orbea lutea subsp. lutea, female Atherigona began by licking small droplets on its outer parts, then moved towards the cavity beneath the guide rails. Inner lobes restricted possible head positions, guiding the head towards the pollination apparatus. [Shuttleworth et al. 2017]
Comparison of insect and flower dimensions showed that small Atherigona fitted into a passage that larger flies had difficulty accessing. This spatial fit explains why some visitors remain on the corolla while a particular insect group actually transfers pollinia. [Shuttleworth et al. 2017]
Three functions of secretory tissues
Colleters secrete mucilage near developing organs. Osmophores participate in synthesising and releasing volatile scent compounds. Nectaries produce secretions associated with feeding the insect and directing its activity towards pollen transfer sites. Position, anatomy and secretion composition determine a gland's assignment to a particular category. [Meve and Liede 1994] [Płachno et al. 2010] [Aliscioni et al. 2024]
Aliscioni and colleagues demonstrated colleters beside sepals, osmophores on the corolla and two locations of tissues interpreted as nectaries, beside the stigmatic chambers and on the inner parts of the corona. They studied microscopic preparations and histochemical reactions indicating substances including mucilage, starch, polysaccharides and terpenes. The article appeared online in June 2023 and in volume 261 of “Protoplasma” in 2024. [Aliscioni et al. 2024]
The material in this paper was described as Ceropegia lenewtonii, with Huernia keniensis also given. In POWO, the first name is a synonym of Huernia lenewtonii, while H. keniensis is an accepted separate species. The anatomical results therefore refer here to the material in the publication. Resolving its identification requires re-examining voucher specimens. Huernia lenewtonii [2-WWW] Huernia keniensis [2-WWW] [Aliscioni et al. 2024]
Surface microstructure
In Orbea variegata, electron microscopy revealed glandular papillae of varied shapes, cuticular striations and pathways for secretion onto the surface. Subepidermal cells and intercellular spaces participate in osmophore organisation. The macroscopically folded corolla is thus also a complex secretory surface active during the flower's life. [Płachno et al. 2010]
Prepared from scientific publications. Accepted names were checked in POWO on 9 October 2026.
Floral biology and pollination in stapeliads — new results and a literature review
Meve U., Liede S., Floral biology and pollination in stapeliads — new results and a literature review, Plant Systematics and Evolution, 1994, 192(1–2):99-116, doi: 10.1007/BF00985911
The study describes the structure of the gynostegium, pollinia and attachment apparatus, and the mechanics of stapeliad pollination by flies. It combines observations with a review of earlier reports. It discusses scent, flower surfaces, nectar and the fit of insect mouthparts to floral structures.
Can a stench be beautiful? – Osmophores in stem-succulent stapeliads (Apocynaceae-Asclepiadoideae-Ceropegieae-Stapeliinae)
Płachno B. J., Świątek P., Szymczak G., Can a stench be beautiful? – Osmophores in stem-succulent stapeliads (Apocynaceae-Asclepiadoideae-Ceropegieae-Stapeliinae), Flora, 2010, 205(2):101-105, doi: 10.1016/j.flora.2009.01.002
A microscopic study of osmophores in Orbea variegata and Boucerosia indica. It describes glandular papillae, subepidermal cells, organelles and routes of secretion release. It explains the anatomical basis for the intense scent of living flowers.
Entering through the narrow gate: A morphological filter explains specialized pollination of a carrion-scented stapeliad
Shuttleworth A., Johnson S. D., Jürgens A., Entering through the narrow gate: A morphological filter explains specialized pollination of a carrion-scented stapeliad, Flora, 2017, 232:92-103, doi: 10.1016/j.flora.2016.09.003
The field study of Orbea lutea subsp. lutea combines fly observations, morphometry, scent analysis and measurements of pollination success. In the population studied, pollinia were carried by females of one Atherigona species whose heads fitted between the corona lobes. The paper shows how a mechanical pollinator filter works.
Colleters, osmophores, and nectaries in the species Ceropegia lenewtonii: a sapromyiophilous stapeliad (Asclepiadoideae, Apocynaceae)
Aliscioni S. S., Gotelli M., Galati B., Zarlavsky G., Torretta J. P., Colleters, osmophores, and nectaries in the species Ceropegia lenewtonii: a sapromyiophilous stapeliad (Asclepiadoideae, Apocynaceae), Protoplasma, 2024, 261(1):3-13, doi: 10.1007/s00709-023-01872-4
A study of the structure and histochemistry of floral glands, including colleters, osmophores and nectaries. The material was described as Ceropegia lenewtonii and equated with Huernia keniensis. In POWO, C. lenewtonii is a synonym of the distinct H. lenewtonii. Attributing the results to a species requires rechecking the material's identification.
