Sciency Thoughts: Menghai County

Friday, 21 June 2019

Cynanchum brevipedunculatum: A new species of Dogbane from Yunnan Province, China.

Dogbanes, Apocyanaceae, are flowing trees, shrubs, herbs, succulents, and vines found in tropical, subtropical and occasionally temperate regions of Europe, Asia, Africa, Australia and the Americas (tree forms are mostly restricted to tropical forests, and sometimes deserts). Many of these plants are toxic, and some have been used to poison Dogs (hence the name), and a number of pharmacological products have been derived from them. Members of the genus Cynanchum are climbers producing white latex, sometimes known as Swallowworts or Dog-stranglers.

In a paper published in the journal Taiwania on 14 June 2019, Jian-Yong Shen, Xing-Da Ma, Wen-Guang Wang, and Ji-Pu Shi of the Xishuangbanna Tropical Botanical Garden describe a new species of Cynanchum from Menghai County in Yunnan Province, China.

The new species is named Cynanchum brevipedunculatum, meaning 'short peduncle' (flower stem), as it has short peduncles. The species is a climber with larger leaves than related species, and shorter flower stems. It produces paired bracts of green and white flowers in November. Only two specimens of the species could be found despite an extensive search, for which reason Shen et al. recommend that the species be classed as Critically Endangered under the terms of the International Union for the Conservation of Nature's Red List of Threatened Species.

Cynanchum brevipedunculatum. (A) Habit. (B)-(C) Adaxial and abaxial leaf surface. (D)-(E) Inflorescences and flowers. (F) Gynostegium in side view. (G) Gynostegium in top view. (H) Pollinarium. Shen et al. (2019).

Meteorites found in Yunnan Province following fireball meteor.

Witnesses in Yunnan Province reported seeing a bright fireball meteor close to the city of Xishuangbanna in the southwest of the province, at about 9.40 pm local time on Friday 1 June 2018. A fireball is defined as a meteor (shooting star) brighter than the planet Venus. These are typically caused by pieces of rock burning up in the atmosphere, but can be the result of man-made space-junk burning up on re-entry. Following the event villagers in Menghai County began reporting meteorite falls, with about 200 such rocks found so far, the largest being about 150 g. At least two of the meteorites caused damage to buildings, and several have been sold online, while local authorities attempt to collect them for scientific research.

Fireball over Yunnan Province on 1 June 2018. APTN.

Objects of this size probably enter the Earth's atmosphere several times a year, though unless they do so over populated areas they are unlikely to be noticed. They are officially described as fireballs if they produce a light brighter than the planet Venus. The brightness of a meteor is caused by friction with the Earth's atmosphere, which is typically far greater than that caused by simple falling, due to the initial trajectory of the object. Such objects typically eventually explode in an airburst called by the friction, causing them to vanish as an luminous object. However this is not the end of the story as such explosions result in the production of a number of smaller objects, which fall to the ground under the influence of gravity (which does not cause the luminescence associated with friction-induced heating).

Fragment of meteorite recovered in Yunnan Province following the 1 June 2018 fireball. Yunnan.cn.

These 'dark objects' do not continue along the path of the original bolide, but neither do they fall directly to the ground, but rather follow a course determined by the atmospheric currents (winds) through which the objects pass. Scientists are able to calculate potential trajectories for hypothetical dark objects derived from meteors using data from weather monitoring services.