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Poaceae
| Gramineae, Poaceae
The Poaceae are mostly herbs comprising one of the largest families of flowering plants with about 500 genera and 8,000 species. The stems are round and commonly hollow, at least in the internodes. The leaves are alternate, and commonly 2-ranked, proximally comprising an open sheathing base with overlapping margins, and distally producing a parallel-veined, strap-shaped blade. On the adaxial leaf surface at the junction of the blade and sheath is an often hairy fringe of tissue called a ligule. The basic unit of the inflorescence is called a spikelet typically consisting of a basal pair of minute sterile bracts called glumes and one or more distichously arranged distal florets on an often zigzag extension of the spikelet axis called the rachilla. Each floret is typically embraced by an additional pair of minute chaffy bracts called the lemma and the palea. The florets are unisexual or bisexual and have usually two or three barely recognizable structures called lodicules that may represent a vestigial whorl of perianth that forces the lemma and palea apart during anthesis, thereby facilitating exsertion of the stamens and stigmas. The androecium typically consists of three or occasionally 6 distinct stamens. The gynoecium consists of a single compound pistil of 2 or sometimes 3 carpels, an equal number of styles with feathery stigmas, and a superior ovary with one locule containing a single subapical to basal ovule. The fruit is usually a caryopsis. |
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