Analyzes on adaptive radiation of semi-desert Asteraceae.

本研究通过两次野外考察，采集了紫草亚科和天牛亚科植物的550个种群样本，对它们的栖息地条件进行了调查，测定了紫草亚科9属100种200个种群的染色体数。在短穗花属和红花花属中发现了频繁的异倍体。干旱地区的物种经常表现出一年生习性，具有复杂的果实结构，如翅膀、膨大的海绵突起和丝状的长毛作为种子的有效散布，这些与较低的染色体数量有关。对天南星亚科23属50种植物的染色体数目进行了测定。虽然在澳大利亚以外的地区，Gnaphalieae的染色体碱基数目在x=7上是恒定的，但在Podolepes(n=12-3)、Pogonolepis(n=6-4)、Rhodanthe(n=11-5)和Tricanthodium(n=4-3)中发现了可变的异倍体系列。为了弄清物种间的亲缘关系以及染色体数目、习性和形态特征的进化趋势，我们比较了不同物种间的RFLP图谱和叶绿体mat K基因的核苷酸序列，构建了短臂藻属的分子系统发育树。这两棵树是一致的，并支持本属的单系。根据花药附属物和花柱的形态、地理分布和染色体数目的变异模式，将其划分为4个类群。异倍体从n=9减少，习性从多年生向一年生转变，果实形态由简单向复杂转变，这些特征被认为是适应干旱或季节性干旱条件的。

We have collected 550 population samples of Australian Astereae and Gnaphalieae and investigated their habitat conditions by two field expeditions.Chromosome numbers from 200 populations attributed 100 species of nine genera of Astereae were determined. The frequent dysploidy has been found in the genera of Brachyscome and Calotis. Species of arid regions frequenthy display an annual habit and have the complex structures of fruit, such as wings, inflated spongy projections and silky long hairs served as the effective seed dispersal, and these are correlated with lower chromosome numbers. Chromosome numbers from 50 species of 23 genera of Gnaphalieae were determined. Although the chromosome base number of Gnaphalieae outside of Australia is constant on x=7, the variable dysploidy series in Podolepes (n=12-3), Pogonolepis (n=6-4), Rhodanthe (n=11-5) and Tricanthodium (n=4-3) were found. To clarify the species relationship and the evlolutionary trends in chromosome number, habit and morphological characters, we have compared the pattern of RFLP and the nucleotide sequence of mat K gene of chlorplast between species and constructed the molecular phylogenetic trees of Brachyscome. Both trees are consistent and support the monophyly of this genus. They also inditate that Brahcyscome is divided into 4 clusters corresponding to the morphology of anther appendage and style, geographical distribution and the variation pattern of chromosome number. The dysploid reductions from n=9, the change of habit from perennial to annual and the change of fruit morphology from simple to complex have been derived in parallel of several lineages and these derived characters are regarded to be adaptive under the arid or seasonally dry conditions.