Morphological and phenological variation in three populations of saffron thistle (Carthamus lanatus L.) from Western Australia

Abstract

Saffron thistle (Carthamus lanatus L.), an erect spiny annual herb, is a weed of pasture and cereal crops in some agricultural areas of southern Australia. Cypselas (achenes or seeds) were collected from mature plants at three sites near Salmon Gums, Moorine Rock and Greenough in Western Australia and grown at South Perth. Two forms were observed and could be distinguished by differences in their phenology and the shape of cotyledons and achenes. After two generations at South Perth, germination in the presence or absence of leaching with water or after storage at daily fluctuating temperatures of 15-60¦C indicated that there were differences between forms as well as between different accessions of the same form. This result suggests that genetic as well as environmental factors influence the breakdown of dormancy and promote germination. Differences in germination were detected when a single accession was sown at two sites, one in the south and the other in the north of the cereal-growing region of Western Australia. Low rainfall and temperatures in autumn were primarily responsible for slow and staggered germination at the more southern site. The protracted germination of saffron thistle in the southern cereal-growing districts creates a problem for cultural control and correct timing of herbicide applications.