BROAD FEATURES OF THE SYSTEM OF ANGIOSPERMS

Abstract

SummaryThe angiosperms are treated as a division Magnoliophyta, with two classes, the Magnoliatae (dicotyledons) and Liliatae (monocotyledons). Takhtajan's six subclasses of Magnoliatae are accepted with only minor alteration. These are the Magnoliidae, Hamamelidae, Caryophyllidae, Dilleniidae, Rosidae, and Asteridae. His four subclasses of Liliatae—the Alismatidae, Arecidae, Commelinidae, and Liliidae—are also accepted, but with a major transfer of the Zingiberales, Bromeliales, Juncales, and Cyperaceae from the Liliidae to the Commelinidae. The aquatic ancestry of the Liliatae has had a profound influence on the subsequent evolutionary history of the group. Loss of cambium, loss of vessels (except for some vestiges in the root), and reduction of the leaf to a phyllode are all probably associated with the ancestral aquatic habitat. The fact that habitai differences are often taxonomically more important among the monocots than they usually are among the dicots reflects the evolutionary difficul. ties under which monocots labor. The single cotyledon of monocots is considered to have arisen by lateral fusion of two, followed by reduction of one of the lobes, and the sheath‐blade structure of the leaves is considered to reflect the cotyledonary structure.