Classification Of Prunus L. Sensu Lato Based On Fruit Morphology

Prunus L.s.l.(Rosaceae),also known as plants of stone fruits,mainly involved Amygdalus L.,Armeniaca Scop.,Prunus L.s.s.,Cerasus Mill.,Padus Mill.,Maddenia Hook.f.& Thomson,Laurocerasus Duhamel and Pygeum Gaertn,probably is composed of 200 ~ 250 species,mostly deciduous trees or shrubs,widely distributed in the north temperate zone,North America,Europe and northern Asia as the main distribution,but also have evergreen tropical species distributed to the old world and new world tropical and subtropical areas.Prunus s.l.is economically important because many species are sources of fruits and nuts(e.g.,P.persica,P.armeniaca,P.salicina,P.mume,P.dulcis,P.avium),oil(e.g.,P.armeniaca,P.dulcis),medicine(e.g.,P.japonica),timber(e.g.,P.serotina)and ornamentals(e.g.,P.serrulata,P.mume).In history,the classification of Prunus s.l.has always been controversial,some scholars advocate its narrow definition,and some advocate its broad definition.In the past 20 years,with the development of molecular phylogeny,the scope of Prunus s.l.has become clear,and many researchers have supported Prunus s.l.to be a clade and its broad definition.However,due to a lack of comprehensive sampling of this group,the subgeneric and interspecific relationships of Prunus s.l.have not yet been reasonably resolved.So,further research of systematic classification of Prunus s.l.is needed.Taking 66 taxa of Prunus s.l.and 1 outgroup of Prinsepia as research object,29 fruit macromorphology were examined and conducted clustering analysis research with UPGMA method(unweighted pair-group method with arithmetic means),combined with fruit epidermal micromorphology,to discuss the generic classification of Prunus s.l.and taxonomic status of some species.The main results are as follows:(1)The fruit morphology of Prunus s.l.has a certain degree of consistency: All are stone fruits;The fruit sulcus is obvious or not obvious;The mesocarp is succulent,no cracking,rare dry and cracking;Most of the endocarp is hard bone,rare thin bone or thin leathery;The shape of the epidermal cells is mostly regular hexagonal,pentagonal,quadrilateral,and the pattern of vertical wall is straight and arched;The stomatal complexes are mostly anomocytic or cyclocytic.The commonalities represent the unification of the characteristics of Prunus s.l.,supporting its genus level.The fruits of outgroup Prinsepia uniflora have no fruit sulcus,with endocarp negatively textured,and its shape of the fruit epidermal cells have more than six sides of polygons,which is different from Prunus s.l..(2)In addition to certain commonalities,there are also certain differences in fruit morphology between various subgenera and taxon of Prunus s.l.,which can better show some specific groups of Prunus s.l.,but there are also overlapping features between some subgeneric groups.In general,the fruit morphology can provide supplementary reference for intergeneric classification and interspecific classification of Prunus s.l.,and has certain taxonomic value.(3)Classification of each subgenus: Based on fruit macromorphology,fruit epidermal micromorphology,combined with other morphological,geographic,and molecular evidence,this paper supports the removal of P.triloba from subgenus Amygdalus(include almonds and peaches);Supports including P.tangutica into Persica(peaches),and compared to Prunus s.s.,the relationship between Persica and the apricot group is even closer;Supports the removal of Microcerasus(dwarf cherries)from Cerasus,together with P.triloba,into Prunus s.s.;The raceme group is nested with subgenus Cerasus,which shows complex evolutionary relationships.(4)Taxonomic discussion of some taxa: Based on fruit macromorphology,fruit epidermal micromorphology,combined with other morphological and geographic evidence,this paper supports merging P.padus var.pubescens into P.padus var.asiatica,merging Maddenia incisoserrata into P.hypoleuca and merging P.hypotricha into P.zippeliana.(5)The epidermal micromorphology of Prunus s.l.not only maintains a certain degree of independence but also shows continuity of morphological evolution.In combination with geographical distribution,the characteristics of vertical wall patterns,stomatal complex types,surface ornamentation and other traits show an evolutionary trend from temperate type to subtropical and tropical types.Vertical walls ranged from straight or arched to more straight and few arched.The stomatal complexes range from anomocytic to cyclocytic and to paracytic,and the surface ornamentation are more or thicker to less or thinner.The research proved that fruit epidermal micromorphology can provide reference for discussing the classification and internal evolution of Prunus s.l.,which is of great significance.