Copyright © 2021 by The American Society of Plant Biologists. The revised classification thus recognizes Chloridoideae and Panicoideae, as indicated in Figure 1. The mighty Himalayas would start to affect Asia’s weather patterns for millions of years. Their work has three major goals. ! The vertical arrangement of the names on the page does not reflect relationship and is chosen generally for convenience only. All the relatives of the grasses similarly accumulate silica somewhere in the plant so that silica accumulation also must have originated well before the grasses themselves did. Because they are in the position of petals and because the early grasses have three, rather than just two, it seems likely that lodicules represent modifications of petals. Florets are borne singly or in groups and are subtended by two more bracts (the glumes). If large enough stretches of DNA can be compared for enough organisms, the phylogenetic relationships generally become clear. This group includes such familiar species as wheat (Triticum), barley (Hordeum), rye (Secale), and oats (Avena), as well as most north temperate lawn and pasture grasses. Studies of ancient ecosystems have shown that these broad areas developed 5 to 6 million years ago. Ribosomal RNA sequences for inferring phylogeny within the grass family (Poaceae). As coarse grasses replace the woodlands during the Oligocene some species evolve larger jaws and deep rooted teeth with protective enamel. The ancestry and origin of the lodicules, palea, lemma, and glumes have been the subject of a vast and largely inconclusive literature. Grass flowers are generally arranged in little spikes, or spikelets; each spikelet consists of one or more flowers plus associated bracts (Fig. Paleoproterozoic (2.5-1.6 billion years ago) The Paleoproterozoic (2.5-1.6 billion years ago) … It is curious that neither Anomochloa nor Streptochaeta, the earliest lineage of the grasses, has either petals or lodicules, although Anomochloa has a ring of hairs outside the stamens (Fig. Some modern mammals appear: advanced primates; camels, cats, dogs, horses & rodents: Paleocene (65 to 54 mya) Flowering plants begin radiation extending through the Eocene. The first is to decipher the evolutionary history, or phylogeny, commonly drawn as a cladogram or branching diagram. In its new circumscription, it represents a much smaller group than it has in the past. Enzymes are boxed. For example, the close relationship of the chloridoid and panicoid grasses, along with other C4 species, suggests the possibility of underlying physiological similarities. ↵* E-mail tkellogg{at}umsl.edu; fax 314–516–6233. Recent work on lodicules in maize and rice has shown that they express petal-identity genes (Ambrose et al., 2000; Kyozuka et al., 2000). Species that are connected by a single branch point (node) are sister taxa. The origin of grass-dominated ecosystems. In the Cenozoic Era, mammals adapted into many different niches. Monocotyledons: Systematics and Evolution, Royal Botanic Gardens, Kew. The original grasses were plants of forest margins or deep shade, characteristics that are retained today inAnomochloa, Streptochaeta, Pharus,Puelia, Guaduella, the bamboos, and the basal pooid, Brachyelytrum. This was between 500 and 600 million years ago. In the grasses, only one locule and one ovule ever form. 2; GPWG, 2000). Reproductive Biology. Given that criterion, we tried to make the named subfamilies as similar as possible to those that previous workers had recognized. The evolutionary tree thus shows that C4 has originated multiple times. A standard for maize genetics nomenclature. Grasses were able to spread due to their ability to dominate arid or drought-prone areas. So even as recently as 420 mya our planet would have looked very different than it does today, and chances are Extensive studies of anatomy, histology, biochemistry, and gene expression have shown that the C4 pathway did not evolve the same way each time it originated (Sinha and Kellogg, 1996). Penny's theoretical work, and Jurkevitch's observations of prokaryotes today, suggest that there were predators on Earth 3.5 billion years ago, very soon after prokaryotic cells first appeared. We have found the fossils of grasses in fossilized dinosaur dung in India, showing that it even had an effect on these huge creatures. The Ginkgoales, a group of gymnosperms with only one surviving species, the Gingko biloba, were the first gymnosperms to appear during the lower Jurassic. The Chloridoideae, including finger millet and tef, was originally recognized by the structure of its microhairs and its C4 anatomy. High seas worldwide. Genera are then assembled into families, and the families are assembled into orders. 1; see also Fig. They were soon joined by bigger grazing mammals as the grasslands carpeted the continents. In the Chloridoideae, on the other hand, all species are C4 but have two layers of cells around the vascular bundles, a characteristic that they share with all their C3 ancestors. In addition, a large set of monocotyledonous plants, including not only the grasses, but also the gingers, pineapples, and palms, have cell walls rich in ferulic acid. The phylogeny correlates well with information from mapping of the nuclear genome (Kellogg, 1998). Grasses: Systematics and Evolution, Commonwealth Scientific and Industrial Research Organization, Collingwood, Victoria. The Paleogene Period* is the first of three periods comprising the Cenozoic Era. These were chosen to represent all known major groups, plus a set of species whose relationships were unknown.