when do bryophytes (including mosses liverworts and hornworts) first appear in the fossil record
Timeline of plant evolution The evidence of plant evolution changes dramatically in the Ordovician with the first extensive appearance of spores in the fossil record (Cambrian spores have been found, also). The first terrestrial plants were probably in the form of tiny plants resembling liverworts when, around the Middle Ordovician, evidence for the beginning of the terrestrialization of the land is found in the form of tetrads of spores with resistant polymers in their outer walls. These early plants did not have conducting tissues, severely limiting their size. They were, in effect, tied to wet terrestrial environments by their inability to conduct water, like extant liverworts, hornworts, and mosses, although they reproduced with spores, important dispersal units that have hard protective outer coatings, allowing for their preservation in the fossil record, in addition to protecting the future offspring against the desiccating environment of life on land. With spores, plants on land could have sent out large numbers of spores that could grow into an adult plant when sufficient environmental moisture was present.
Wolffia Wolffia is a genus of nine to 11 species which include the smallest flowering plants on Earth. Commonly called watermeal or duckweed, these aquatic plants resemble specks of cornmeal floating on the water. Wolffia species are free-floating thalli, green or yellow-green, and without roots. The flower is produced in a depression on the top surface of the plant body. It has one stamen and one pistil. Individuals often float together in pairs or form floating mats with related plants, such as Lemna and Spirodela species. Most species have a very wide distribution across several continents. Wolffia species are composed of about 40% protein on a dry-matter basis, about the same as the soybean, making them a potential high-protein human food source. They have historically been collected from the water and eaten as a vegetable in much of Asia. The genus was first recorded in New Zealand by Ruth Mason.[1]