Grasses, the plant family Gramineae, first showed up in the Early Cenozoic, specifically i

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Grasses, the plant family _Gramineae_, first showed up in the Early Cenozoic, specifically in the Paleogene (sometime in the Early Paleocene). They did not reach their full ecological potential until the Late Oligocene and Miocene, however. Early grasses were apparently confined to wooded or swampy areas. Like modern sedges that form the marshlands along coastal areas, the mode of growth of early grasses did not allow their leaves to grow continuously and thus to recover from heavy grazing by animals of the type that inhabit open country in large numbers. It was only by virtue of an adaptive breakthrough - the origination of continuous growth - that grasses were ultimately able to invade open country with great success. Once they were able to survive the effects of heavy grazing by animals, grasses spread quickly over vast expanses of the Earth to form grasslands. Since you asked (remember, you DID ask...), there is another interesting evolutionary point to consider in the development of grasses: with the enormous numbers of individual grass plants populating marshes and grasslands, effective reproduction would be damned high impossible if these plants required pollination by insects. Thus, it comes as no surprize that grasses are wind-pollinated (much to the chagrin of allergy sufferers) plants. But, it should be noted that grasses can carpet large areas by means of budding (through tillers and rhizomes), a non-sexual reproductive strategy in which individuals send out subterrestrial runners that sprout new plants, thus rapidly and densely colonizing and stabilizing the soil and driving to distraction homeowners who must deal with crabgrass...

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