Plants of Central Asia - Plant Collection from China and Mongolia Vol. 13: Plumbaginaceae, Oleaceae, Buddlejaceae, Gentianaceae, Menyanthaceae, Apocynaceae, Asclepiadaceae PDF

PREFACE

This volume covers the treatment of 7 families of gamopetalous flowering plants: Plumbaginaceae Juss. (7 genera, 41 species), Oleaceae Hoffmgg. (3, 6), Buddlejaceae Wilh. (1, 5), Gentianaceae Juss. (8, 111), Menyanthaceae Dum. (2, 2), Apocynaceae Juss. (1, 2) and Asclepiadaceae R. Br. (2, 14). In all, these families comprise 24 genera and 180 species, with 34 of them being endemics and 30 subendemics. To these should be added one more genus (Psylliostachys Nevski) with 21 species (including 6 endemics) from the Central Asian part of the erstwhile USSR, thus bringing the total number of species inhabiting the entire Central Asia will be 201; 40 of these, or 20%, are endemics.

Of the families treated in this volume, the largest and the important in the flora are gentians (Gentianaceae) and leadworts (Plumbaginaceae). These 2 families represent antipodes in the ecological and coenotic context: while gentians are mesophytes and predominantly inhabit alpine meadows, leadworts are desert and arid-steppe xero- and halophytes. Among gentians, only Gentiana dahurica, G. decumbens and G. olivieri can be termed as steppe inhabitants. Gentians in Central Asia are representatives and derivatives of East Asian flora, only 10 of them being endemics (11%). Quite naturally, maximum diversity among gentians is noticed on the eastern fringe of Central Asia — in Qinghai and northeastern Tibet (Weitzan) as well as in Tien Shan. All of the endemics are concentrated here.

Leadworts, however, represent Mediterranean flora and are rich in local endemics: of the 41 species of leadworts, 18 or 44% are endemics and, on adding to them the 11 subendemic species, endemism rises to 70% ! Genus Limonium Mill. contains the maximum number of endemic species: of the 23 species, 13 are endemics and 5 subendemics.

The coenotic importance of both these families in the vegetative cover of Central Asia is not of much significance. Many gentians are highly ornamental plants and add colour to the alpine meadows while a few of 4 them sometimes make for a colourful scenario, as for example Gentiana barbata in the wet coastal meadows.

Massive growth of some species of leadworts of genus Limonium make up their own scenario: L. bicolor (pink inflorescence) in the steppes of Eastern Mongolia and L. tenellum (blue) and L. aureum (lemon-yellow) in desert steppes and deserts of Mongolia. Species of Acantholimon Boiss. occupy a prominent position in the pillow structures of Tien Shan, Pamir and western Tibet.

Representatives of rest of 5 families are few, rare and very limited in their spread. Only dogbane (Apocynum L.) and some swallowworts (Cynanchum L. of Asclepiadaceae) are extensively distributed. A. venatum and A. pictum, inhabitants of solonchaks, are found in all desert regions from Junggar and Kashgar to Alashan and Qinghai. Liana Cynanchum sibiricum is widely distributed in the oases of Central Asia while C thesioides (= Vincetoxicum sibiricum) is a common sight in desert and arid steppes of Mongolia and southern Siberia. The rest of members of this large family represent only rare inhabitants of East Asia, mainly in the border regions: some of them like Periploca sepium and Cynanchum bungei are distinct relicts while others, for example C. chinense, are confined to their own distribution range. C. gobicum, C. komarovii and C pusillum have, however, succeeded in developing into local endemics here.

The family of olives is represented in Central Asia by 3 Chinese species of lilac in Alashan mountain range and mountains of Qinghai and are of relict type: Mediterranean jasmine (Jasminum officinale) and 2 species of Mediterranean ash, Fraxinus sogdiana in tugais of Junggar and Kashgar and Himalayan F. xanthoxyloides found in extreme southwestern Tibet.

The large (over a hundred species) East Asian, predominantly tropical genus Buddleja L. is represented by the lone Chinese species B. alternifolia, a relict of Alashan mountain range and Eastern Qinghai and 4 species in south-eastern Tibet in Lhasa region, having reached there from East- Tibet and eastern Himalayas. One of them is a local derivative-endemic (B. wardii). Menyanthes trifoliata and Nymphoides peltatum represent boreal, marsh and coastal-aquatic, extensively distributed species.

Among the chronologically interesting data is the distribution of Tibet- Qinghai species of gentians: annual Gentiana arenaria Maxim., reported quite recently from Central Tien Shan (Sarydzhas river basin) and G. saposhnikovii Pachom., detected and described as a new species (1986). It is possible that, the latter, like Circaeaster agrestis Maxim. from among buttercups, will be found in the Himalayas too (the plant is small and escapes detection) which would once again confirm the historic links between Tien Shan and Tibet through the Himalayas.

The distribution of leadworts is of interest. Several species of leadworts form well-distinguished, distinct botanical-geographic limits of different ranks. Thus, for example, Limonium tenellium (Turcz.) Ktze. is an endemic of Mongolia with its distribution covering its entire Gobi territory while L. roborowskii Ik.-Gal. is an endemic of Kashgar with distribution coinciding with its boundaries. The distribution of L. myrianthum (Schrenk) Ktze. encompasses the whole of Junggar-North Turan province from Aralo-Caspian region in the west of Junggar Gobi in the east; that of  L. aureum (L.) Hill covers the entire Mongolian- Chinese Central Asia, barring Sinkiang. Acantholimon alatavicum Bge. 5 marks the mountainous Junggar and A. kokandense Bge. only Western Kashgar.