sir/maim

“Do I have Ortus’s eyes? Are these ones mine? I never really looked at them— Beloved, what were my eyes like?”

F E R N PRAIRIES

seriously, there were lots of different kinds of prairies. fern, horsetail, cycad, the list goes on. Basically, different kinds of low-lying plants would do the prairie thing in ecosystems where forests couldn't get a foothold.

but, there were a lot fewer of them than today. because grasses are kind of OP, and have their own photosynthesis system, so they are able to grow and take over many places that would have been forests before grasses took over. That doesn't mean there weren't prairies, but there were just less. and a lot of things were more scrubland than prairie, too.

C4 grasses dominate the tropics but in higher latitudes the dominant grasses have same type of photosynthesis as almost all other plants (and there are non-grass C4 photosynthesizers too).

grasses are generally dominant wherever trees are suppressed. biggest suppressors are disturbances like fire and herbivory (how grazing mammals feed is different than most dinosaurs) and rainfall too low to support trees. it also helps grasses are wind-pollinated which has great synergy with the above and with the increasing seasonality we see over the Cenozoic. the herbivory aspect is frequtently ignored but shouldn't be imo, studies with white rhinos demonstrated that if rhinos were excluded, grasses decreased

i say generally because there are exceptions and they tend to have traits that put them more in line with how Mesozoic communities were:

Here is a fern field in Hawai'i an area with no native grazing herbivores (but decent disturbance rate due to volcanoes so openings occur anyway) + constant humidity + tropical climate. I've seen parts of South FL like this as well and FL has many Cretaceous floral elements

Prior to grasses, at least before Cenozoic, ferns likely were the dominant plant in disturbed areas. Cycads and other gymnosperms were important back then too but I have yet to find examples of some that took on more grass-like ecological roles

Most ferns during Mesozoic are NOT closely related to the ones we see today. ~80-90% of ferns we see today belong to Polyopsid group which emerged at the earliest 100 mya.

Some of the older fern groups get pretty weird with some even looking grass-like:

Schizae pusilla of New Jersey, Shizaea is part of a very old group of ferns. There are other species e.g. in South Africa and that one I know is more adapted to seasonally dry conditions.

similarly old horesetails being quite dominant:

montane and poor soil ecosystems which naturally exclude megaherbivores tend to be dominated by woody shrubs or non-grass herbaceous plants e.g. Fynbos in Southern Africa, rift scrub in Rwanda, various Australian ridges, moorland and heath in Europe, sagebrush in North America, all the whacky paramo guys so those are good sources of inspiration too even if they lean more on angiosperms