Starch Grains of Endosperm in Grass Systematics

Abstract

During the past 80 years occasional attention has been paid to the structural features of starch grains of endosperm in connection with the systematic grouping of grasses. Harzl' was the first to recognize that different types of starch grains have a systematic value. He disclosed that the starch grains of grass endosperm can be divided into three types : compound grains, flat simple grains with round or ellip-tic shape, and simple spherical grains with or without angles. Harz believed that natural tribes should be uniform as to the features of starch grains, and referred even to the parallel development of morphological characters. The starch features were taken up by Hackel2', Krause3' and Hayek4' in their discussion on grass sys-tematics or evolution, although Harz's division into three types was replaced by a simpler division into two types, simple and compound. Avdulov5' carefully reviewed the features of starch grains appearing in the preceding papers and compared them with his cytological findings. Avdulov discovered that the features of starch grains are not always exactly correlated in the major taxonomic groups (subfamilies) with other basic characters of systematic significance which he studied; those of chromosome number and morphology and of leaf anatomy. Therefore, Harz's and Hayek's suggestions were not accepted. Nevertheless, Avdulov advocated that the starch features have some value in systematics and used them in the subdivision of the subfamily Poatae. The opinion that natural tribes are uniform as to starch features was not upset. Starch grains of several controversial grass genera were examined by some subsequent investigatorsfi-8' when they studied the affinities of the species of those genera. A few recent authors9-11' also examined the starch grains of some particular groups as a part of their taxonomic studies. The conclusions of these authors were based upon the assumption that two types should be recognized in the starch grains of grass endosperm and that the festucoid grasses (except Triticeae, Bromus and Brachypodium) and the eragrostoid grasses possess compound grains., whereas the panicoid grasses, as well as Triticeae, Bromus and Brachypodium, have simple grains. Stebbins and Crampton'2', who discussed the significance of various characters used in the systematics of Gramineae, estimated the structure of starch grains as the character moderately important. No comprehensive survey of starch grains of grasses has been made after Avdulov5', however. Some contradictory results to this common opinion were obtained by the present author and were reported in Japanese13-r4'. These preliminary studies suggested that the common opinion regarding the relationship of starch grain structure to :systematics might depend on insufficient observations or adjustment of the data to non-phylogenetic system. Although starch grain data from a total of 424 species were given in Avdulov's6' list, there was a natural overemphasis on the Festucoideae. Moreover, in Panicoideae the records of starch grains appearing in Avdulov's list demonstrate that some panicoid grass species do not have simple starch grains.