Phylum Magnoliophyta (Flowering Plants)

Abstract

The characteristic features of the phylum (division) of Magnoliophyta are: (1) ovules are enclosed in a more or less completely closed cavity formed by one or by several to many separate or united carpels; (2) pollen grains are deposited not directly on the micropyle of the ovule but on the stigmatic surface, which is capable not only of receiving the pollen but also of assisting in the development of the pollen tube (initially the stig-matic surface stretches along more or less free carpel-lary margins, but in the majority of flowering plants it is localized and forms a specialized stigma); (3) both male and female gametophytes are devoid of gametan-gia (antheridia and archegonia) and are extremely sim-plified and specialized; (4) triple fusion: one of the two male gametes fuses with the egg cell (syngamy), and the other with two free or already fused polar nuclei of the central cell of the female gametophyte; as a result of triple fusion a diploid zygote and a triploid primary nucleus of the endosperm are formed; although in the Podostemaceae and Orchidaceae the endosperm fails to develop or degenerates early in ontogeny, the triple fusion is a characteristic feature of magnoliophytes, sharply distinguishing them from all other plants; (5) sieve elements with companion cells.