Monoplastidic meiosis in Dumortiera hirsuta (Bryophyta; marchantiales)

The early sporocyte of Dumortiera hirsuta contains a single large plastid. Plastid division occurs in advance of nuclear division and the four resulta nt plastids migrate to the future spore domains. In many cases, the four da ughter plastids continued to divide before nuclear division. The cytoplasm becomes shallowly lobed around the four domains and each domain contains at least one plastid. Positioning of plastids and cytoplasmic lobing seem to establish the meiotic division planes before nuclear division. Monoplastidi c meiosis, which can be considered to be a symplesiomorphic character, is t ypical of mosses and hornworts but is known only sporadically in isolated t axa of liverworts. Meiosis of Dumortiera seems to represent an evolutionary stage that is transitional between monoplastidic and polyplastidic meiosis .