Origins of an alpine flora: The evolution of high mountain floras is strongly influenced by tectonic and climatic history. Dinget al.document the timing, tempo, and mode by which the world's most species-rich alpine flora, that of the Tibet-Himalaya-Hengduan region, was assembled. Alpine assemblages in the region are older than previously thought, with lineages tracing their alpine ancestry to the early Oligocene—older than any other modern alpine system. Alpine species diversified faster during periods of orogeny and intensification of the Asian monsoon, and the Hengduan Mountains—the most species-rich area in this region—played a key biogeographic role as the location of the earliest pulse of alpine diversification in the Oligocene.Science, this issue p.578

We reconstruct the rise of a segment of the southern flank of the Himalaya-Tibet orogen, to the south of the Lhasa terrane, using a paleoaltimeter based on paleoenthalpy encoded in fossil leaves from two new assemblages in southern Tibet (Liuqu and Qiabulin) and four previously known floras from the Himalaya foreland basin. U-Pb dating of zircons constrains the Liuqu flora to the latest Paleocene (ca. 56 Ma) and the Qiabulin flora to the earliest Miocene (21–19 Ma). The proto-Himalaya grew slowly against a high (∼4 km) proto–Tibetan Plateau from ∼1 km in the late Paleocene to ∼2.3 km at the beginning of the Miocene, and achieved at least ∼5.5 km by ca. 15 Ma. Contrasting precipitation patterns between the Himalaya-Tibet edifice and the Himalaya foreland basin for the past ∼56 m.y. show progressive drying across southern Tibet, seemingly linked to the uplift of the Himalaya orogen.

The often-used phrase ‘the uplift of the Tibetan Plateau’ implies a flat-surfaced Tibet rose as a coherent entity, and that uplift was driven entirely by the collision and northward movement of India. Here, we argue that these are misconceptions derived in large part from simplistic geodynamic and climate modeling, as well as proxy misinterpretation. The growth of Tibet was a complex process involving mostly Mesozoic collisions of several Gondwanan terranes with Asia, thickening the crust and generating complex relief before the arrival of India. In this review, Earth system modeling, paleoaltimetry proxies and fossil finds contribute to a new synthetic view of the topographic evolution of Tibet. A notable feature overlooked in previous models of plateau formation was the persistence through much of the Cenozoic of a wide east–west orientated deep central valley, and the formation of a plateau occurred only in the late Neogene through compression and internal sedimentation.

The youngest palm fossil record in Tibet suggests that there was no high Tibetan Plateau until the Neogene.