Permian floras became much more
xerophytic as the global climate shifted from cold
to warm. Tropical regions dried out as rainfall seasonality increased.
Only in what is now China did tropical rain forests and peat-forming
swamps persist into the Late Permian. With this drying a whole new
suite of plants appeared, expanding into many areas of the lowland
landscape. Many of these plants had probably been living in Pennsylvanian-age
upland regions, where soils were better drained than in the lower
wetlands and rainfall may have been more seasonal. Climatic zonation
was pronounced, however, and floras from different climatic belts
were markedly distinct.
In addition, competition in these drier areas may have led to diversification
and greater variability among seed-bearing plants. Plants may also
have begun to evolve in response to the fact that they now had to
survive the onslaught of new, abundant vertebrate herbivores. The
Permian was rich in conifers (Walchia, Ernestiodendron),
cycad-like plants (Taeniopteris, Russellites),
gigantopterids (Gigantopteridium, Cathaysiopteris,
Zeilleropteris, etc.), and callipterids (Autunia,
Rachiphyllum). Most of these were seed producing. Limited
wet spots persisted, identified by the occurrences of tree fern
foliage, calamites (especially along stream banks),
and rare tree lycopsids (Sigillaria).