The orchid family is renowned for its enormous diversity of pollination mechanisms and unusually high occurrence of non-rewarding flowers compared to other plant families. The mechanisms of deception in orchids include generalized food deception, food-deceptive floral mimicry, brood-site imitation, shelter imitation, pseudoantagonism, rendezvous attraction and sexual deception. Generalized food deception is the most common mechanism (reported in 38 genera) followed by sexual deception (18 genera). Floral deception in orchids has been intensively studied since Darwin, but the evolution of non-rewarding flowers still presents a major puzzle for evolutionary biology. The two principal hypotheses as to how deception could increase fitness in plants are (i) reallocation of resources associated with reward production to flowering and seed production, and (ii) higher levels of cross-pollination due to pollinators visiting fewer flowers on non-rewarding plants, resulting in more outcrossed progeny and more efficient pollen export. Biologists have also tried to explain why deception is overrepresented in the orchid family. These explanations include: (i) efficient removal and deposition of pollinaria from orchid flowers in a single pollinator visit, thus obviating the need for rewards to entice multiple visits from pollinators; (ii) efficient transport of orchid pollen, thus requiring less reward-induced pollinator constancy; (iii) low-density populations in many orchids, thus limiting the learning of associations of floral phenotypes and rewards by pollinators; (iv) packaging of pollen in pollinaria with limited carry-over from flower to flower, thus increasing the risks of geitonogamous self-pollination when pollinators visit many flowers on rewarding plants. All of these general and orchid-specific hypotheses are difficult to reconcile with the well-established pattern for rewardlessness to result in low pollinator visitation rates and consequently low levels of fruit production. Arguments that deception evolves because rewards are costly are particularly problematic in that small amounts of nectar are unlikely to have a significant effect on the energy budget of orchids, and because reproduction in orchids is often severely pollen-, rather than resource-limited. Several recent experimental studies have shown that deception promotes cross-pollination, but it remains unknown whether actual outcrossing rates are generally higher in deceptive orchids. Our review of the literature shows that there is currently no evidence that deceptive orchids carry higher levels of genetic load (an indirect measure of outcrossing rate) than their rewarding counterparts. Cross-pollination does, however, result in dramatic increases in seed quality in almost all orchids and has the potential to increase pollen export (by reducing pollen discounting). We suggest that floral deception is particularly beneficial, because of its promotion of outcrossing, when pollinators are abundant, but that when pollinators are consistently rare, selection may favour a nectar reward or a shift to autopollination. Given that nectar-rewardlessness is likely to have been the ancestral condition in orchids and yet is evolutionarily labile, more attention will need to be given to explanations as to why deception constitutes an 'evolutionarily stable strategy'.

Mechanisms and evolution of deceptive pollination in orchids

http://www.hummingbirds.arizona.edu/Faculty/Dornhaus/courses/read_ECOL567/Waser%20syndromes.pdf

A global test of the pollination syndrome hypothesis.

The Asclepiadaceae, as traditionally defined, have repeatedly been shown to be an apomorphic derivative of the Apocynaceae. It has often been recommended that the Asclepiadaceae be subsumed within the Apocynaceae in order to make the latter monophyletic. To date, however, no comprehensive, unified classification has been established. Here we provide a unified classification for the Apocynaceae, which consists of 424 genera distributed among five subfamilies: Rauvolfioideae, Apocynoideae, Periplocoideae, Secamonoideae, and Asclepiadoideae. Keys to the subfamilies and tribes are provided, with lists of genera that (as far as we have been able to ascertain) are recognized in each tribe.

/pdf/a-revised-classification-of-the-apocynaceae-s-l-1oq9xj0bpn.pdf

A revised classification of the Apocynaceae s.l.

Evolution of protein molecules. I. Protein synthesis

The concept of a generalist flower appears to mean different things to different people, depending upon their background and training We assess the different meanings of generalist flowers with respect to the ecological "set and setting" of pollination, and then we discuss notions of ecological, functional and phenotypic generalization These ideas are explored in more detail using examples from our own published and unpublished studies on the pollination ecology of Daucus carota, Hedera helix, and Chamerion angustifolium, and from the published work of other researchers Finally we relate these ideas and clarified definitions of "generalist" and "specialist" flowers to the pollination syndrome concept

Multiple meanings and modes: on the many ways to be a generalist flower

The myiophilous pollination syndrome of stapeliads is investigated. Olfactory stimuli, imitating dung or decaying organic (zoogenic or phytogenic) matter, are used as attractants, together with mimetic colouration and, sometimes mimetic sculpturing. In most species nectar is present. The nectar mainly serves as optical attractant causing brilliance effects, and as visitor guide. However, nectar obviously is also a reward in many species. Flies (Cyclorrhapha:Calyptratae) constitute the most important pollinating group. In the pollination process they carry pollinaria only at the distal parts of their proboscis, never on their legs. No fundamental differences between the pollinator spectra of flowers in habitat and cultivated ones were observed.

Floral biology and pollination in stapeliads — new results and a literature review

Representatives of nearly all genera of the taxon-rich stem-succulent stapeliads and most of the few related, leafy genera were analyzed. Sequence data from two non-coding molecular markers (ITS region of nrDNA and trnT-L and trnL-F spacers as well as the trnL intron of cpDNA) support the traditional tribal affiliation of the genera, which form a monophyletic group. This monophylum breaks into a basal Neoschumannia/Anisotoma/Riocreuxia/Sisyranthus nk;clade, from which the core Ceropegieae are derived. The four Ceropegia species included are not monophyletic, and their relationship to Brachystelma changes depending on the marker studied. The stem succulent taxa fall in a number of well supported, but unresolved clades, the most prominent being the predominantly southern African clade comprising Orbea, Stapelia and some other genera. The most derived taxa of NE Africa, Duvaliandra and White-sloanea, are basal to this southern African clade. The other clades comprise the more basal genera of stem-succulent stapeliads, including the members of the Caralluma complex. Of the 17 genera accepted by Plowes for the Caralluma complex, seven are recognized: Caralluma, Apteranthes, Australluma, Boucerosia, Caudanthera, Desmidorchis and Monolluma. New combinations are proposed in 15 cases; Caralluma adscendens var. geniculata is raised to specific rank. Anomalluma is reinstated, and Pseudolithos mccoyi is transfered to it. A broadened concept for Orbea (incl. Angolluma and Orbeopsis) is recognized, but Orbeanthus is kept separate. The monotypic Ballyanthus, recently separated from Orbea, is nested within Duvalia. Piaranthus (incl. Huerniopsis) is monophyletic. The bitypic Notechidnopsis is reduced to the type species, N. tessellata, while N. columnaris is transferred to a new genus, Richtersveldia.

A molecular phylogeny and generic rearrangement of the stapelioid Ceropegieae (Apocynaceae-Asclepiadoideae)

Analysis of the trnT-trnL spacer, the trnL intron and the trnL-trnF spacer of 65 species of Cynanchum, 33 members of the Metastelminae, and seven representatives of other Asclepiadeae shows that Cynanchum in its present circumscription is polyphyletic. Both the genus Cynanchum and the subtribe Metastelminae s.l. split along the Old World—New World geographic division. The only exception to this division is Cynanchum subgenus Mellichampia, which belongs to Cynanchum s. str. For the Old World Cynanchum relatives, the subtribe Cynanchinae is re-established. The remaining New World sections of Cynanchum are not monophyletic. The South American members of section Cynanchum join the morphologically aberrant Grisebachiella hieronymi. Section Macbridea is associated with Funastrum. In the Old World, the succulent genera Folotsia, Karimbolea, Platykeleba, and Sarcostemma are monophyletic with stem-succulent Cynanchum and nested within a clade of exclusively Malagasy Cynanchum species. Communicating Editor...

https://bioone.org/journals/systematic-botany/volume-27/issue-4/0363-6445-27.4.789/Circumscription-of-the-Genus-Cynanchum-ApocynaceaeAsclepiadoideae/10.1043/0363-6445-27.4.789.pdf

Circumscription of the Genus Cynanchum (Apocynaceae—Asclepiadoideae)

Monophyly and sister group relationship of Ceropegieae and Marsdenieae, the two Asclepiadoideae tribes possessing erect pollinia, are confirmed by molecular investigation of non-coding cpDNA markers (trnT-L and trnL-F spacers, and the trnL intron). In Ceropegieae, the analyzed taxa fall in four subclades. The Heterostemma subclade is sister to other three subclades, of which the Conomitra-Leptadenia-Orthanthera subclade is sister to the Anisotoma-Neoschumannia-Riocreuxia-Sisyranthus subclade and to the large subclade comprising the stem-succulent stapeliads, Brachystelma and Ceropegia. Following these results, subdivision of Ceropegieae into four subtribes, Anisotominae, Heterostemminae, Leptadeniinae and Stapeliinae, is proposed.

Subtribal division of Ceropegieae (Apocynaceae­Asclepiadoideae)

On the basis of morphological and chemical data, the genus Vincetoxicum is recognized as separate from Cynanchum. Tylophora is identified as the closest relative of Vincetoxicum. In consequence, eleven new combinations in Vincetoxicum are proposed. The C. auriculatum group is recognized as C. sect. Rhodostegiella. Tylophoropsis must be included in Tylophora, which results in one new combination.

Sigrid Liede

Papers

Floral biology and pollination in stapeliads — new results and a literature review

A molecular phylogeny and generic rearrangement of the stapelioid Ceropegieae (Apocynaceae-Asclepiadoideae)

Circumscription of the Genus Cynanchum (Apocynaceae—Asclepiadoideae)

Subtribal division of Ceropegieae (ApocynaceaeAsclepiadoideae)

Cynanchum. Rhodostegiella. Vincetoxicum. Tylophora (Asclepiadaceae) : New considerations on an old problem

Sigrid Liede

Papers

Floral biology and pollination in stapeliads — new results and a literature review

A molecular phylogeny and generic rearrangement of the stapelioid Ceropegieae (Apocynaceae-Asclepiadoideae)

Circumscription of the Genus Cynanchum (Apocynaceae—Asclepiadoideae)

Subtribal division of Ceropegieae (Apocynaceae­Asclepiadoideae)

Cynanchum. Rhodostegiella. Vincetoxicum. Tylophora (Asclepiadaceae) : New considerations on an old problem

Subtribal division of Ceropegieae (ApocynaceaeAsclepiadoideae)