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- Jörgensen, Annelie, et al.
(författare)
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Reproductive morphology in the Gnetum cuspidatum group (Gnetales) and its implications for pollination biology in the Gnetales
- 2015
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Ingår i: Plant Ecology and Evolution. - : Agentschap Plantentuin Meise. - 2032-3913 .- 2032-3921. ; 148:3, s. 387-396
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Tidskriftsartikel (refereegranskat)abstract
- Background and aims - The Gnetales include the extant genera Gnetum, Ephedra and Welwitschia. They are usually functionally dioecious, but male cones often have sterile (but pollination drop-producing) ovules in addition to male units. There are, however, exceptions, i.e. most species of Ephedra and African species of Gnetum. Furthermore, the literature contains conflicting information on the Asian Gnetum cuspidatum. One study states that sterile ovules are present in this species; another that they are absent. The latter also claims that male cones secrete nectar instead, which is interesting because nectar has only been suggested to be present in four gymnosperm species. Here we aim to elucidate whether or not sterile ovules are present in male cones of G. cuspidatum and related taxa, evaluate evidence for nectar being present in gymnosperms and discuss implications for pollination biology. Methods - Male cones from relevant taxa were examined using a dissecting microscope and scanning electron microscopy. Key results - Sterile ovules are present in G. cuspidatum and the related G. macrostachyum, G. microcarpum, G. diminutum and G. loerzingii, but they are minute, hidden among hairs, and easily overlooked. No indications of nectar or nectaries were found and their presence in Asian species of Gnetum is questioned. Conclusions - Insect pollination is probably ancestral in the Gnetales. Like most species of Gnetum, members of the G. cuspidatum group have sterile ovules in male cones, and they can thus attract pollinators to both male and female plants using sweet pollination drops. Although it is possible that these species, in addition, produce extraovular reward for pollinators, we find no such evidence. Instead, it seems plausible that pollination drops have been mistaken for (extraovular) nectar. However, African species of Gnetum have unisexual male cones. Have they developed another means of pollinator reward in male plants or are they wind-pollinated as are their ephedran analogues?
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| 2. |
- Persson, Nannie L., et al.
(författare)
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Phylogenetic relationships of the 'Briza complex' to other members of the subfamily Pooideae (Poaceae)
- 2016
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Ingår i: Plant Ecology and Evolution. - : Agentschap Plantentuin Meise. - 2032-3913 .- 2032-3921. ; 149:2, s. 216-227
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Tidskriftsartikel (refereegranskat)abstract
- Background and aims - The species of the 'Briza complex' (Pooideae, Poaceae) are distributed in South America and Eurasia. They are relatively well-studied morphologically and have a complex taxonomic history, but only a few phylogenetic studies have been conducted using molecular data. Monophyly of the complex, which is based on presence of 'brizoid' spikelets, has not been questioned and sampling strategies in previous studies have prevented assessments thereof. Methods - We investigate phylogeny and node ages in the Briza complex and test monophyly of the group using nuclear and chloroplast data. Extensive sampling from the Briza complex and putatively related species in the subfamily Pooideae is employed. Key results - Despite morphological similarity among species, the Briza complex is polyphyletic. Members were found in three different Glades, showing the South American species, the Eurasian species and Briza humilis to be distinct groups. The South American and the Eurasian clades originated about 11 and 13 million years ago, respectively. Briza humilis diverged from Phleum (or a related genus) about 10 million years ago, whereas its crown clade is from the Pliocene-Pleistocene border. The almost simultaneous origins of these clades in the mid-Miocene coincide with temporal estimates of major diversification in grasses and formation of grassland habitats. Conclusions - Based on our results, we support the names Chascolytrum for the South American Glade and Briza for the Eurasian clade. For the Briza humilis clade, we propose the name Brizochloa. The parallel evolution of (seemingly) similar 'brizoid' spikelets in the Pooideae is surprising; however, studies have shown that floral morphology can alter dramatically by one-step mutations, causing evolutionarily distantly related species to have similar appearance. Our findings may hopefully inspire new morphological investigations of the species of the former Briza complex, as well as other poorly studied and potentially polyphyletic genera, such as Deschampsia and Echinopogon.
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