|Publication Type:||Book Chapter|
|Year of Publication:||1995|
|Authors:||Endress, P. K.|
|Editor:||Cribb, P. J., Cutler, D. F., Humphries C. J.|
|Book Title:||Monocotyledons: systematics and evolution|
|Publisher:||Royal Botanic Gardens, Kew|
Recurrent floral traits present in more than one superorder of monocots but less frequent or even absent from dicots are discussed. The frequent sectorial association of tepals and stamens may be partly related to the frequent occurence of common organ primordia. Common organ primordia also occur among tangentially associated organs, such as in orchids and Zingiberales, which has made the morphological interpretation of the lip of these monosymmetric flowers difficult. The potential of extensive intercalary growth has led to the evolution of "amphibious" flowers with the pollination organs in the air, but the ovary either under water or underground. Septal nectaries are an almost exclusive monocot feature; but tepal nectaries are also rather common. Both features may occur in closely related groups, rarely even in the same genus. In contrast to the disc nectaries of dicots both septal and tepal nectaries of monocots seem to lack stomata; rather, nectar is secreted by the epidermis. Grasses have the most elaborate anemophilous flowers among the monocots. Their close relationship with Joinvilleaceae and Restionaceae is supported by some special floral traits, especially the unique complex plumose stigma. Spathes and large bracts are often associated with condensed inflorescences and they may be intimately synorganized in various ways, the most extreme being the aroid pitcher traps. Although flowers with trimerous organ whorls are common and are probably basal in the monocots, there are many groups with increased or decreased stamen or carpel numbers, the greatest lability being in Alismatanae and Arecanae, both with up to several hundred organs. Floral organ arrangements is whorled or irregular, but apparently never regularly spiral. It is suggested that in both groups that have been thought to represent the most basal monocots (i.e. Alismatanae and Lilianae) the most obvious floral similarities with dicots (i.e. Nympheales and Aristolochiales) have been shaped by similar ecological conditions (aquatic habitat and sapromyophily) and are not necessarily based on very close bauplan relationships.