Monday, 29 December 2014

A new species of Chinese Arborvitae from the Late Miocene of Yunnan Province.

The Chinese Arborvitae, Platycladus orientalis, is a species of Cypress widely grown as an ornamental plant in China, North Korea and the Russian Far East. Its precise origin is unknown, though it is thought to be native to Gansu, Hebei, Shaanxi and Shanxi Provinces. Genetic studies have suggested that the last common ancestor that it shared with its closest known relative, Microbiota decussate, lived about 33 million years ago in the Early Oligocene.

In a paper published in the journal PLoS One on 17 December 2014, Jing-Yu Wu of the Key Laboratory of Mineral Resources in Western China at the School of Earth Sciences and College of Earth and Environmental Sciences at LanzhouUniversity and the State Key Laboratory of Palaeobiology and Stratigraphy at the Nanjing Institute of Geology and Paleontology, and Su-Ting Ding, Qi-Jia Li, Zhen-Rui Zhao and Bai-Nian Sun, also of the Key Laboratory of Mineral Resources in Western China, describe a new species of Platycladus from the Late Miocene Nanlin Formation in Lianghe County in Yunnan Province.

The new species is named Platycladus yunnanensis, meaning ‘from Yunnan’. It is described from eight specimens, all of flattened splays of foliage preserved in mud- and siltstones, from which it was possible to extract some of the material for examination under a light microscope.

Folliage branch of Platycladus yunnanensis in matrix. Scale bar is 1 cm. Wu & Ding et al. (2014).

These are the oldest specimens of Platycladusor Microbiotaknown (specimens of Microbiota have been reported from the Pliocene of Russia), and Wu & Ding et al. are able to confidently date the deposits that produced them to between 6.77 and 7.20 million years old, using potassium/argon isotope dating of basalt layers above and below the sediments. Argon-Potasium dating relies on determining the ratio of radioactive Potasium⁴⁰ to Argon⁴⁰ within minerals from igneous or metamorphic rock to determine how long ago the mineral cooled sufficiently to crystalize. Potasium⁴⁰ is often incorporated into cooling volcanic rocks, whereas any inert Argon present will escape as a gas. No further Potasium⁴⁰ or Argon⁴⁰ will enter the mineral from this point, but Argon⁴⁰ is produced by the decay of radioactive Potassium⁴⁰ at a steady rate, enabling scientists to establish a precise date for the crystalization of the minerals containing the two elements.

Foliage branch of the extant Platycladus orientalis. Scale bar is 1 cm. Wu & Ding et al. (2014).

The modern Platycladusorientalisis thought to be native to areas of China far cooler and drier than Yunnan Province, though it will live there and has naturalised in parts of the province and neighbouring Sichaun. Platycladus yunnanensisis essentially similar to the modern Platycladus orientalis, though it does have open stomatal pits and shallowly sunken guard cells, which are generally considered to be adaptations to a warm, moist climate, as would be predicted for the Late Miocene of Yunnan Province.

(C) Outer view of the stomatal zone in the abaxial cuticle of facial leafof Platycladus yunnanensis, showing the Florin rings. (D) Outer view of the stomata in the abaxial cuticle of lateral leaf, showing the elliptical stomatal pit and surrounding Florin ring. Wu & Ding et al. (2014).

See also…

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