New insight on the formation of East Asian flora

Wu & Wu (1996) first proposed the former "Eastern Asiatic region" to be an independent floristic Kingdom, the "East Asiatic Floristic Kingdom". It is significant to the definition of the Floristic regions of the world. However, there are still some questions need to be discussed.

These are floristic regions of the Eastern Asiatic Floristic Kingdom and its two subkingdoms (A & B) based
on Wu and Wu (1996) (7). White dashed lines (A) demarcate boundaries of two floristic subkingdoms;
Photos of living plants (B) are the representatives of each subkingdom; (a) Gentiana, (b) Corydalis,
(c) Primula, (d) Pedicularis, (e) Rhodiola, (f) Saxifraga, (g) Rhododendron, (h) Eucommia,
(i) Cercidiphyllum, (j) Ginkgo, (k) Trochodendron, (l) Cathaya, (m) Davidia, (n) Metasequoia
[Credit: © Science China Press]

As many living fossil plants (Cenozoic plant relicts) only occurred in East Asian today, many researchers have suggested that the East Asiatic Floristic is an ancient flora and the cradle of North American, European floras and even the modern Paleo-tropical flora .

In addition, East Asia has also been considered to be the diversification or origin center of angiosperms. Besides this, as most paleoendemic taxa of the East Asiatic Floristic occurred in the Sino-Japanese flora and neoendemic taxa were concentrated in the Sino-Himalayan flora. Previous studies suggested that the Sino-Japanese flora is older than the Sino-Himalayan flora. Are these hypothesis true or not? However, until today these questions have not been solved well, due to the limitation of research methods and materials.

On the basis of previous studies, Prof. Sun Hang's Group from Kunming Institute of Botany, Chinese Academy of Sciences (KIB/CAS), propose the term "Metasequoia Flora" to represent the core area of the Sino-Japanese Flora. Since the living fossil plant Metasequoia glyptostroboides is one representative of the relicts or living fossil lineages that are found in this area. Similarly, They propose the term "Rhododendron Flora" to better represent the core region of the Sino-Himalayan flora, as Rhododendron is the largest genus and formed a diversity center in this region, plus it is a representative plant of the flora in this area.

These are geographical origins of the East Asian flora. Pie chart illustrate the percent of taxa originated in situ,
ambiguous origin and immigrants from other flora. Arrows indicate the biogeographical origin of East Asian
elements from other region. Photos of living plants are the representatives of different geographical origins;
 (a) Cyananthus, (b) Cotinus, (c) Rhodiola, (d) Ilex, (e) Stachyuraceae, (f) Hamamelis, (g) Coriaria,
(h) Helleborus, (i) Mandragora, (j) Cissus, (k) Hypericum, (l) Viburnum, (m) Musa, (n) Alangium,
(o) Myriophyllum, (p) Disporum, (q) Carya, (r) Schima, (s) Rhus, (t) Adenocaulon, (u) Smilax,
 (v) Diapensia, (w) Cassiope [Credit: © Science China Press]

On the basis above, the group first synthesized published molecular phylogenetic data as well as fossil information on the seed plants, try to trace the temporal and spatial evolution of East Asian flora by integrating these datasets with paleo environmental studies that are related to this area.

The results suggest that the East Asian might be relatively young, with most of its clades originating since the Miocene, it should be the refugia for ancient relict plants rather than the birthplace. The Rhododendron Flora and the Metasequoia Flora are probably of a similar age.

The formation and development of the Asian monsoon might have been the main factors that drive the evolution of East Asian flora. The unequal distribution of species diversity in Rhododendron and Metasequoia flora may be due to the diverse and heterogeneous topography and climate of this region caused by the uplift of Qinghai-Tibetan Plateau. Meanwhile, this phenomenon may be also correlated with the direction of mountains ranges in these regions. The East Asian flora appears to have multiple biogeographical origins, being closely affiliations not only with other floras in the Northern Hemisphere, but also with Gondwanan floras.

The study results are published in National Science Review.

Source: Science China Press [February 27, 2018]