Widespread chromosome variation in the endangered grassland forb Rutidosis leptorrhynchoides F. Muell. (Asteraceae: Gnaphalieae)

Rutidosis leptorrhynchoides is an endangered plant endemic to southeastern Australia. Chromosome analysis of 19 of the 24 known populations of the species has identified 17 different chromosome variants or cytotypes. The most common cytotypes are a diploid and a tetraploid based on x = 11, and triploid and hexaploid plants with this basic number were also observed. Diploids, triploids and tetraploids based on a second basic number of x = 13 were also seen. Plants with 2n = 24 were shown to be hybrids between diploids with the two different basic numbers. Meiotic chromosome pairing analysis of the plants with 2n = 24 showed a maximum of two trivalents indicating the presence of extra copies of one pair of large and one pair of small chromosomes in the 2n = 26 plants. In addition, a number of different aneuploids of the 2n = 22 and 2n = 44 races were found and many of these also showed structural chromosomal variation. The distribution of the two main chromosome races is disjunct with the tetraploids confined to southern Victoria. To avoid dysgenic effects, future re-establishment efforts for this species should avoid mixing seed from different chromosome races. (C) 2000 Annals of Botany Company.