Holttumochloa has previously only been recorded from Malaysia. Here we describe and illustrate a new species, Holttumochloa hainanensis sp. nov., from the lowland montane forests of Diaoluo Mountain on the Island of Hainan, South China. Morphologically, H. hainanensis is similar to Holttumochloa korbuensis, but can be clearly distinguished from it in having larger culms covered by white wax, longer leaf blades, larger pseudospikelets and anthers. Furthermore, molecular phylogeny based on the nuclear gene GBSSI corroborates the identification of the new species and its affinity. The biogeographical significance of the new record of Holttumochloa in South China is also highlighted in this study.
Stratification in lowland rainforests of Meghalaya, India, which represent the westernmost limit of the rainforests north of the Tropic of Cancer, was studied in horizontal and vertical planes to elucidate the patterns in stacking of species diversity and community attributes, and to draw comparisons with rainforests of 'Indo-Malaya' ecozone (biogeographical realm). All individuals ≥10 cm GBH (girth at breast height) were enumerated in six transects of 10 m width and up to 500 m length covering 2.45 ha area. The stratification of whole assemblage of species in vertical plane is referred to as 'storey structure' (=height class distribution), which explains structural complexity. In horizontal plane, it is typically referred to as 'stand structure' (=girth class distribution), which explains structural heterogeneity. The stratification of an individual species in vertical plane is referred to as 'loftiness' and in horizontal plane, it is frequently referred to as 'population structure'. The stand structure was characterized by a negative exponential relationship or a reverse J-shaped curve, which is typical of a well regenerating forest stand. The storey structure was characterized by the low stature of the rainforest (<30 m), subtle layering in the canopy with dearth of discrete multi-stories, narrower widths of the stories and a thick understory. The cluster analysis and 'candlestick charts' showed that the dominant species spatially segregated in canopy height to profile three strata, viz., an understory of juveniles and shrubs below 5 m, a middle-storey of intermediate trees between 5 and 15 m, and an overstory of large trees between 15 and 25 m. Emergent trees of a few species may reach up to 30 m. The individuals tended to scatter in increasingly wider range of height classes from a lower to the next higher girth class, creating a 'torchlight scatter' pattern, with a tendency to concentrate towards smaller height classes due to stochastic factors, which potentially influence vertical growth proportionate to diametric growth. In comparison to equatorial rainforests of Malaysia and seasonal rainforests of southwestern China, the rainforests of Meghalaya are short-statured at the geographic extremity of the occurrence of rainforest biome in Asia-Pacific region, owing to floristic composition, site quality factors, excessively higher quantities of rainfall and high differential of precipitation and potential evapotranspiration. Despite limited diversity of megaphanerophytes, these rainforests deserve concerted conservation efforts as they stack high diversity of meso-, micro- and nano-phanerophytes.
Yunnan in southwestern China is renowned for its high plant diversity. To understand how this modern botanical richness formed, it is critical to investigate the past biodiversity throughout the geological time. In this review, we present a summary on plant diversity, floristics and climates in the Cenozoic of Yunnan and document their changes, by compiling published palaeobotanical sources. Our review demonstrates that thus far a total of 386 fossil species of ferns, gymnosperms and angiosperms belonging to 170 genera within 66 families have been reported from the Cenozoic, particularly the Neogene, of Yunnan. Angiosperms display the highest richness represented by 353 species grouped into 155 genera within 60 families, with Fagaceae, Fabaceae, Lauraceae and Juglandaceae being the most diversified. Most of the families and genera recorded as fossils still occur in Yunnan, but seven genera have disappeared, including Berryophyllum, Cedrelospermum, Cedrus, Palaeocarya, Podocarpium, Sequoia and Wataria. The regional extinction of these genera is commonly referred to an aridification of the dry season associated with Asian monsoon development. Floristic analyses indicate that in the late Miocene, Yunnan had three floristic regions: a northern subtropical floristic region in the northeast, a subtropical floristic region in the east, and a tropical floristic region in the southwest. In the late Pliocene, Yunnan saw two kinds of floristic regions: a subalpine floristic region in the northwest, and two subtropical floristic regions separately in the southwest and the eastern center. These floristic concepts are verified by results from our areal type analyses which suggest that in the Miocene southwestern Yunnan supported the most Pantropic elements, while in the Pliocene southwestern Yunnan had abundant Tropical Asia (Indo-Malaysia) type and East Asia and North America disjunct type that were absent from northwestern Yunnan. From the late Miocene to late Pliocene through to the present, floristic composition and vegetation types changed markedly, presumably in response to altitude changes and coeval global cooling. An integration of palaeoclimate data suggests that during the Neogene Yunnan was warmer and wetter than today. Moreover, northern Yunnan witnessed a pronounced temperature decline, while southern Yunnan experienced only moderate temperature changes. Summer precipitation was consistently higher than winter precipitation, suggesting a rainfall seasonality. This summary on palaeoclimates helps us to understand under what conditions plant diversity occurred and evolved in Yunnan throughout the Cenozoic.