AN ATTEMPT AT THE CONSTRUCTION OF A SYSTEM OF THE GENUS PARIETARIA AND RELATED FORMS (MATERIALS FOR A MONOGRAPH)

Abstract

The present paper contains a brief presentation of the results obtained bу the study of the genus Parietaria sensu lato. The inflorescence in this group represents a combined type of cymose. From the base the inflorescence developsonthe dichasium plan; farther on one of the axesof the dichasium is suppressed remaining rudimentary and therefore the terminal branches of the inflorescence represent a typical cincinna. The flowers of the part of the inflorescence forming a dichasium are provided with one bract. In the cincinna this single bract is joined by a second one which is a secondary formation of one of the rudimentary axes. The terminal flowers have three bracts of which one is a normal bract, while the other two have originated from two rudimentary lateral axes (Fig. 1). As to the disposition of the flowers in the inflorescence 2 types may be distinguished. In the first type the flowers of the dichasium (with only one bract) are pistillate, while those of the cincinna (with 2—3 bracts) are androgynous. This is the type of the genus Parietaria sensu stricto (Fig. 3). In this genus the bases of the bracts are often coalescent and the axes of the inflorescence are rudimentary (Fig. 2). Sometimes in § Parietariella all flowers are androgynous. In the second type the flowers of the dichasium are androgynous and those of the cincinna pistillate (Fig. 4). This is the genus Freirea. Gaud. The second marked character distinguishing the genus Parietaria from the genus Freirea is the presence of a long style in the former and a sessile stigma (absence of a style) in the second. The genus Parietaria is distributed in the Mediterranean and comprises annual and perennial forms. The genus Freirea is distributed in the temperate zone of both hemispheres and consisting exclusively of annuals. Within the limits of Parietaria and Freirea sections are established. The structure of the inflorescence in the different sections and species of the genus Parietaria are taken as a basis for generalization of phylogenetic character. The most primitive type was found in P. erecta which is ecologically confined to broadleaved woods which may be considered as relicts. From the type subsect. Monocyma the shortened inflorescence of Pycnocyme is derived. The species of Monocyma are annuals, of the same type within an area of great extension and ancient. The species of subsect. Руспосута are partly annuals (P. cretica L.) and present a number of geographical races (P. officinalis L. and related forms). Section Parietariella is the youngest forming numerous local races (the types § P. judaica Strand.) and has separated from section Euparietaria by way of suppression of the basal pistillate flowers of the inflorescence. A comparison of the morphological variety and geographical distribution of the different sections of the genera Parietaria and Freirea and their collation with other genera of the tribe Parietaria reveals the existence of a hiatus between them requiring that the first two genera should be separated from each other.