Evolutionary history of plants and radially symmetrical, is an integumented megasporangium surrounded by a cupule. The megasporangium bears an unopened distal extension protruding above the multilobed integument. It is suspected that the extension was involved in anemophilous pollination. "Runcaria" sheds new light on the sequence of character acquisition leading to the seed. "Runcaria" has all of the qualities of seed plants except for a solid seed coat and a system to guide the pollen to the ovule. The first spermatophytes (literally: "seed plants") – that is, the first plants to bear true seeds – are called pteridosperms: literally, "seed ferns", so called because their
Evolutionary history of plants to C. This ratio is denoted . C plants are on average around 14‰ (parts per thousand) lighter than the atmospheric ratio, while C plants are about 28‰ lighter. The of CAM plants depends on the percentage of carbon fixed at night relative to what is fixed in the day, being closer to C plants if they fix most carbon in the day and closer to C plants if they fix all their carbon at night. Original fossil material in sufficient quantity to analyse the grass itself is scarce, but horses provide a good proxy. They were globally widespread in