Bio430

AngiospermFamilies

Angiosperms possess the most recently derived synapomorphies that provide strong support for their monophyly, and have contributed to their high levels of diversification compared to other plant groups. In angiosperms, seeds are enclosed in ovaries that mature into fruit; strobili are modified into flowers typically with both sterile and fertile parts. Like gymnosperms, they heterosporous, with tiny microgametophytes (pollen grains) developing just 2 sperm each. Megagametophytes are also reduced, often to just 7 cells with 8 nuclei. Fertilization involves both sperm: one fuses with the egg to form the new sporophyte embryo, while the other fuses with two nuclei in a central cell of the female gametophyte to form endosperm--the food source for the developing embryo. Other angiosperm features include vessels in their xylem, phloem seive and companion cells sharing a developmental origin, and a double integument. Angiosperms vary from woody shrubs to trees, vines and liannas, herbacious long-lived perennials, and annuals. Seeds are enclosed in carpels (that make up ovaries) so that they are not exposed to the environment at the time of pollination.