Reproductive Systems

Abstract

Reproductive systems in the grasses are diverse. This section begins by describing the morphological variation in placement of the stamens and pistils, and then follows with discussion of outcrossing, self-pollination and apomixis. UNISEXUAL VS. BISEXUAL FLOWERSGrasses may have unisexual or bisexual flowers. Because of the distribution of the unisexual versus bisexual condition in the immediate outgroups and early diverging taxa, attempts to determine the ancestral condition for the family are highly sensitive to analytical method and assumptions (Malcomber and Kellogg 2006). Among the graminid Poales, flowers of Flagellariaceae are bisexual, whereas those of Restionaceae, Centrolepidaceae and Anarthriaceae are unisexual. The two immediate outgroups of the grasses, Ecdeiocoleaceae and Joinvilleaceae, have unisexual and bisexual flowers, respectively. In the grasses, flowers in Anomochlooideae are bisexual, but those in Pharoideae are unisexual, and Puelioideae are bisexual. This distribution of character states indicates either that unisexual flowers have arisen repeatedly, or that reversion from unisexual to bisexual is fairly easy over evolutionary time, or both.Virtually all possible arrangements of unisexual flowers on the plant are known in the grasses (Connor 1981(Connor , 1987. Monoecy is widespread, appearing in all Pharoideae, tribe Olyreae of Bambusoideae, many members of Chloridoideae and Panicoideae, and some Ehrhartoideae. Among monoecious grasses, sex expression may vary between flowers within a spikelet (e.g., Lecomtella, Ixophorus), between spikelets within an inflorescence (e.g., Pharus, Hypogynium, Zizania), or between inflorescences within a plant (e. g., Zea, many Olyreae).Andromonoecy is common, particularly in the Panicoideae, in which spikelets are conventionally two-flowered, with the lower flower often producing stamens and the upper one being bisexual. Additional variations on this theme occur in the tribe Andropogoneae, with sex expression varying between the flowers in each of the two spikelets of the spikelet pair. For example, in many species of Andropogon, the sessile spikelet has a sterile lower flower and bisexual upper flower, while the pedicellate spikelet has a sterile lower flower and staminate upper one; this produces an inflorescence of bisexual and staminate flowers in a 1:1 ratio. In other Andropogoneae (e.g., Elymandra), the most proximal spikelet pairs on the inflorescence consist entirely of staminate flowers, thus increasing the ratio of staminate to bisexual flowers.In contrast to andromonoecy, gynomonoecy is rare in the grasses as a whole. Connor (1981) reports only eight genera with this distribution of flower types. In two of these, the bambusoids Diandrolyra and Piresia, the apparently bisexual flowers are in fact staminate with the gynoecium non-functional; thus, the plants are actually monoecious. In the chloridoid genus Munroa, pistillate flowers are proximal to bisexual ones in the spikelets of most species, but in M. squarrosa, pistillate spikelets occur only...

Did apomixis evolve from sex or was it the other way around?

“…Despite frequent events of genomic repatterning and gene losses, which have caused considerable divergence in genome size in the grass family (Bennetzen and Wang, 2018), genes have tended to maintain their position in chromosomes with strict conservation of gene order (collinearity) or gene co-localization (synteny) (Wang et al, 2015 and references therein). Since grass genomes are largely syntenic and apomixis occurs throughout the grass family, several authors have thought that the same set of genes may control apomixis in grasses (Kellogg, 2015). However, while the regions controlling apomixis are similar within genera (Pupilli et al, 2004;Akiyama et al, 2011), they can be highly divergent between genera (Ozias-Akins, 2006).…”

Epigenetic‐induced alterations in sex‐ratios in response to climate change: An epigenetic trap?

“…switch from floral development to vegetative development) that leads to the formation of leafy shoots or bulbils . Transitions between pseudovivipary and sexual reproduction have been observed in both directions in experimental set ups and in natural populations . While flower reversion has been traditionally explained by genetic causes, Wang et al showed that in rice pseudovivipary is, at least partly, regulated by an epigenetic mutation.…”