A Taxonomic Revision Of Microtropis (Celastraceae)

Microtropis Wall.ex Meisner,a medium genus of the family Celastraceae,currently contains about 60-70 species in the world,which are distributing in East and Southeast Asia,and Central American.Although this is no a large genus,but from the day when it is established,the names published under this genus are numerous,but have no yet been well treated for even one time in the worldwide scale.Due to the complex of variation in the morphological characters and the difficulties of observation of the small flowers,the classification of this genus is very difficult and there are many problems in the present species under this genus.Therefore,the work to conduct a comprehensive revision of this genus is very necessary.By studying on more than 3000 sheets of specimens in herbaria and observing of more than 20 populations in fields,we tried to search and evaluate the variation patterns of morphological characters amang the Microtropis plants.The results show that the good characters for taxonomy concentrates on flowers.Inflorescence types and branching times,calyx shape and texture,petal shape, disk state and its condition with petals and stamens,anther shape,and pistil shape are the most important characters in the genus.But we also found that the development of flowers in this genus is very slow and the phase from the beginning of inflorescence primordium to mature or opening of the flowers is often more than 6 months,there are conspicuous differences of flower characters between the materials collected at different phases,and there are still pseudohermaphroditic and diecious phenomenons in some species,so the practical use of flower characters are somewhat limited.The leaf shape and texture,and the fruit shape and size are also very important characters for taxonomy, but variable due to different habitat and different developmental stages.It is noteworthy that the populations of the same species from different geographical locations often show conspicuous and gradual variation in various characters.Therefore,the taxonomy of such a genus must use as many characters as possible,can no rely on a few characters. Leaf architecture features of 16 taxa in Microtropis were studied.The results show that thegeneral features of leaf architecture are quite uniform as camptodromous pinnate venation.Intraspecific the divergence angle of secondary veins,and the density of tertiary veins or higher veins are quite variable,thus are inappropriate for species discrimination.Whereas the number and shape(straight or arcuate) of secondary veins,and the state of vein areolas are quite different and stable between different species,so can be used as characters for taxonomy.Foliar epidermis of 67 taxa in Microtropis and 4 related genera was observed with SEM.The results show that the comeous layer is very thick,the structure of epidermal cells can't be distinguished,the stomas are irregularly arranged on the lower surface of leaves.Sculpture can be devided as 3 types,smooth,striate,and papillate.Striate sculpture and papillate sculpture are specialized characters,and only occur in a few species.Generally,there are not significant differences of foliar epidermis between the genera observed.Pollen of 39 taxa in Microtropis and 3 related genera was observed with SEM.The results show that most pollen grains observed are elliptoid,globose,or oblong at equatorial view,tricolporate, extine layer foveolate or reticulate.In most species the pollen grains are only slightly different in the size,but a few Malaysian species have specialized pollen grains which are irregular in shape and closely arranged to form structure like pollen mass.Generally,the pollen grains show not significant differences between the genera observed except the size.Finally,a taxonomic revision of the genus Microtropis worldwide was conducted,based on extensive literature survey,both herbarium and field observations,and experimental evidences.The genus Quetzalia Lundell(1970) with central American species are included in Microtropis,and total 47 species in Microtropis worldwide have been accepted,the gross distribution in the countries as following: China 18,Malaysia 15,Indonesia 8,Vietnam 8,India 5,Philippines 5,Myanmar 4,Thailands 4,Sri Lanka 2,Mexico 2,Japan 1,Bangladesh 1,Bhutan 1,Costa Rica 1,Guatemala 1,Cambodia 1,Laos 1, Brunei 1.3 new species M.daweishanensis Q.W.Lin et Z.X.Zhang,M.longicarpa Q.W.Lin et Z.X.Zhang,and M.xizangensis Q.W.Lin et Z.X.Zhang from China are described.M.caudata, M.fasciculata,M.macrocarpa,M.philippinensis,M.rubra,and M.javanica are recognized as independent species,other 47 names are reduced to synonyms.7 taxa are recognized as not Microtropis plants,in which new nomenclature Glyptopetalum integrifolium Q.W.Lin,Z.X.Zhang et Q.R.Liu(Basonym:M.poilanei Tardieu) and new combination Garcinia gagei(Merr.et Freeman) Q.W.Lin et Z.X.Zhang(Basonym:M.gagei Merr.et Freeman) were proposed. M.fallax,M.macrophylla,and M.pallens recorded in Chinese literature are confirmed as misidentification,M.macrocarpa is confirmed as endangered species endemic to China,and M.rhynchocarpa is newly record in Guangdong,China.Finally,there are still 3 names which are lack of any materials and can only be left to be done later.