sites, Arabis fecunda begins flowering in early to mid-April, and 

 mature fruit is present beginning in mid-May. Seed dispersal 

 begins in late May. In Beaverhead and Silver Bow counties, 

 flowering at the lower elevation sites occurs in mid-May through 

 early June, and mature fruit can be found starting in early June. 

 At sites near or above 7,000 ft, mature fruit can be found 

 starting in mid- June. Flowering and fruit maturation depends on 

 weather conditions in that year. 



2. POPULATION SIZE AND CONDITION: Five of the known 

 A. fecunda populations have fewer than 1,000 

 plants, seven populations have between 1,000 and 

 10,000 plants, and six have more than 10,000 

 plants. Population estimates for all known sites 

 are given in Table 4. Most populations appear 

 vigorous with plants of all sizes present, 



3. REPRODUCTIVE BIOLOGY 



a. TYPE OF REPRODUCTION: Arabis fecunda 

 reproduces from seed only. Seed is only 

 produced following pollination (Walsh 1992) , 

 suggesting that agamospermy does not occur; 

 however, pseudogamy cannot be ruled out, 



b. POLLINATION BIOLOGY: Walsh (1992) reports 

 that Arabis fecunda is fully self-compatible. 

 In nature, seed is probably a result of a 

 combination of selfing and outcrossing. 

 Results of an isozyme genetics study are 

 consistent with a mixed mating system (Leeper 

 et al., in press). It is not known what 

 proportion of the seeds are the result of 

 self-pollination. 



Pollinating agents of Arabis fecunda are not 

 known. Plants flowers very early in the 

 growing season; thus, the most likely 

 pollinators are flies which are the only 

 common vectors at that time of year. Mathew 

 Hamilton (pers comm.) reported flies visiting 

 A. fecunda flowers at Charleys Gulch in 1990. 



c. SEED BIOLOGY: In 1989-93 the number of seeds 

 per fruit for Arabis fecunda at one site in 

 Ravalli County and two sites in Beaverhead 

 County varied between 5 and 56 with a five- 

 year mean that varied between 31 and 34 

 (Lesica and Shelly 1994) . Reproductive 

 plants produced 0-96 fruits with a mean of 

 10.6-14.6 at the three sites (Lesica and 

 Shelly 1994) . Number of seeds and fruits 



15 



