Taxonomic Revision And Flora On The Genus Macromitrium In Northern South America

Orthotrichaceae is the third largest moss family in the world in tern of species number.The family is not only a transitional taxon from the acrocarpous mosses to pleurocarpous mosses,but also has a key position in Musci because of its special peristome structure.Macromitrium is the largest genus in the family Orthotrichaceae,also the third largest genus within moss taxa.Because Macromitrium(as wllas other genera such as Macrocoma,Orthotrichum ect.)have been found as polyphyletic groups,we are not able to conduct a systematic study on Macromitrium.Therefore,there is not yet preliminary and widely recognized classification system about the family Orthotrichaceae.The northern South America(including Colombia,Guyana,and French Guiana,Suriname and Venezuela)is one of the regions with highest diversity of the genus Macromitrium in the world.Within the focal area existed 52 accepted species names of Macromitrium.Among these species names,23 had been described before the mid 19 th century without very brief and obscure descriptions on some morphological characters.No systematic and authoritative revisions about these species names.Therefore,a taxonomic revision on the species of Macromitrium in Northern South America is urgently needed,which is very important for construction of a natural classification system of Orthotrichaceae.Macromitrium is distinguished mainly by the creeping,prostrate stems giving rise to branches terminated by sporophytes;the leaves are twisted and contorted around the branches,mostly with bulging,conic,uni-papillose or pluri-papillose median and upper cells,or tuberculate lower and basal cells;calyptrae are large,mitrate or cucullate,plicate,naked or hairy;ovate to cylindric capsules mostly have peristomes,which are often reduced and fused,forming a low,single exostomial membrane.It is a typical pantropical group,mostly growing on trees and scarcely on rocks.In the present paper,we extensively checked the original literature about Macromitrium,and about 1,000 specimens including 53 types from 17 herbaria around the world.We finished a taxonomic revision of the genus Macromitrium in Northern South America based on these herbarium specimens,as well as conducted a quantitative study of Macromitrium micrstomum(Hook.& Grev.)Schw?gr.)on its morphological variation pattern by using Cluster Analysis and the Detrended Correspondance Analysis(short for DCA).The main results are as follows:1.All of the 52 species names were checked based on their type specimens,the morphological characteristic were clearly given by line drawing.Based on our taxonomical revision,thirteen new synonyms of Macromitrium have been found,which include M.catharinense Paris(= M.drewii H.Rob),M.crenulatum Hampe =(M.longifolium(Hook.)Brid.),M.crosbyorum B.H.Allen & Vitt(=M.aureum Müll.Hal.),M.emarginatum Broth.(= M.pellucidum Mitt.),M.flexuosum Mitt(=M.constrictum Hampe & Lorentz),M.gigasporum Herzog(= M.frondosum Mitt.),M.subscabrumMitt.(= M.constrictum Hampe & Lorentz),M.trinitense R.S.Williams(= M.scoparium Mitt.),M.subnitidum Hal.Müll.(= M.microstomum(Hook.& Grev.)Schw?gr.),M.filicaule Hal.Müll.(= M.microstomum(Hook.& Grev.)Schw?gr.),M.pacificum var.brevisetum Thér.=(M.microstomum(Hook.& Grev.)chw?gr.),M.pacificum var.longisetum Thér.= M.microstomum(Hook.& Grev.)Schw?gr.).So far thirty-eight species have been confirmed by our present taxonomical revision.2.According to dry status of plants,the length,shape,apex,costa of branch leaves,the layer of upper leaf cells,shape,length-width ratio and surface characteristics of different parts of leaf cells,differentiation or not of basal leaf cells,the cell boundary,thickness of cell wall,and capsule shape,surface,and caplytra characteristics,we proposed a key to identify these 41 species of Macromitrium in Northern South America.3.Macromitrium microstomum(Hook.& Grev.)Schw?gr.is the most widespread species of the genus in the world and exhibits highly morphological variations as evident by the inclusion of its many synonyms.Our preliminary comparison of M.microstomum with M.subnitidum Hal.Müll.,reported from Venezuela and other relevant species showed a high similarity among them.A quantitative study of 98 relevant specimens,including 17 types from its synonyms was carried out to test and understand the patterns of morphological variation within the species.Data of 63 morphological traits were used to construct a dendroogram and a two-dimensional scatter plot to reveal their morphological variation patterns,which were further revealed visually by compiling figures of digitalized branch leaves and perichaetila leaves.Our quantitative analyses show that variation coefficients differ enormously ranging from 0.187 to 0.647 among morphological traits,especially for the branch leaves in terms of leaf length,length/width ratios at median and upper parts as well as the angles of leaf apex.The average variation coefficient of the morphological indices is larger in perichaetial leaves than in branch leaves.Other variations from sporophytic traits,such as the width at capsule mouth and seta length of M.microstomum were also analysed.Although the overall morphological variations are continuous among 98 specimens of M.microstomum,our study shows that variations do exist among specimens from different geographical regions,particularly in morphological traits obtained from leaf angles and leaf length.Macromitrium subnitidum Müll.Hal.,M.filicaule Müll.Hal.,M.pacificum var.brevisetum Thér.and M.pacificum var.longisetum Thér.are four new synonyms of M.microstomum.