Concepts about development of the plant component of New World terrestrial ecosystems through deep time have reached a point where it is possible to consider some subtle and refining details about the process. One such detail is the temporal relationship between the opportunity of new habitats provided by the physical processes of landscape development and long-term climate change, and the availability of the mostly angiosperm lineages that presently occupy these habitats. Some habitats (e.g., beach/strand/dune) were in existence long before the rise of the flowering plants ca. 125 million years ago (Ma), and some did not develop until late in the Neogene from a combination of cooling climates and locally to regionally increasing elevations (alpine tundra/páramo). In other instances, both habitats and lineages existed contemporaneously, but in different parts of the world, so development of the particular ecosystem had to await the appearance and spread in the New World of the lineage through migration (e.g., Rhizophora L. into modern mangrove habitats after the Late Eocene; Quercus L. from the north into modern oak–Weinmannia L. habitats only after 330 thousand years ago (Kyr). The temporal correspondence between opportunity and availability joins the more widely recognized forcing mechanisms of geologic and climate change, acting on evolutionary processes, as one additional factor in better understanding the origin, composition, and distribution of the ecosystems that presently characterize the New World.