Monocots

Abstract

Abstract The monocots are a strongly supported monophyletic group comprising about 25% of the angiosperm diversity. 7ey number 59,300 species (1) and are classiAed in 81 families and 10 orders by the Angiosperm Phylogeny Group (APGII) (2). A number of morphological characters are shared by most monocots, although these may have been (secondarily) lost in some lineages. thesingle cotyledon, leaves with linear venation, a basal meristem, scattered vascular bundles in the shoots and a lack of secondary growth of xylem and phloem, and sieve cell plastids are among the most obvious shared-derived morphological characters. Monocots usually possess trimerous Powers and uniaperturate pollen, which is most commonly monosulcate. Monocot characters also appear in other angiosperm groups. For example, sieve cell plastids occur in some Aristolochiaceae, scattered vascular bundles in Nymphaeaceae and some Piperaceae, and trimerous Powers with two perianth whorls are present in Nymphaeaceae and some magnoliids. Several monocots from diBerent orders and families do have reticulate venation. 7is is, however, a derived condition thought to represent an adaptation to shaded habitats such as the forest understorey.