More info for the terms: caudex
Small burnet establishes from seed [127,156] and by sprouting from the caudex [79,117]. Some plants may sprout from rhizomes [115,116].
Pollination: Small burnet is pollinated by bees .
Breeding system: Small burnet populations in North America are mostly derived from European stock selected for rapid seedling establishment and growth, high seed production, cold tolerance, and high forage value for wildlife and livestock [58,81,89,146]. Because of founder effects and subsequent breedings in the United States to enhance only these traits, overall genetic diversity of North American populations is probably low compared to native European populations.
Small burnet is monoecious . Rarely, it is also apomictic [87,109].
Flower and seed production: Small burnet first flowers and sets seed at 2 years of age .
Small burnet produces seed prolifically on mesic sites . In dryland pastures on the San Juan Basin Research Center, Colorado, small burnet was the highest seed producer among 11 species tested. Across 3 years, mean small burnet seed production ranged from 623 to 1,307 seeds/3 mÂ² . Small burnet generally does not reproduce in the most xeric areas of the Great Basin .
Herbivorous animals can reduce small burnet's ability to reproduce from seed . Ungulates, lagomorphs, granivorous rodents, and grasshoppers sometimes consume small burnet seeds so heavily that there is little net seed production [127,152]. Small burnet usually produces seed on such sites when rodent and lagomorph populations are low and/or when livestock grazing is controlled. Dense grass stands also impair small burnet's ability to set seed and persist in wildlands .
Seed dispersal: Small burnet seed remains in the hypanthium when dispersed. Hypanthia are dispersed by animals, and possibly by wind and water. In the Great Basin, small burnet has established from unretreived seed in rodent caches . The wings on most small burnet hypanthia may facilitate wind and/or water dispersal; speculation on the function of the wings was not found in the literature. In a study of flooded meadow communities in France, small burnet was present in soil seed banks on riverbanks subjected to periodic, short-term floods . Small burnet is reported mostly from shorelines in Michigan . These studies raise the possibility that water disperses small burnet hypanthia.
Seed banking: Small burnet has a persistent soil seed bank [67,99,141,147,147]. Studies in northwestern Europe found viable small burnet seed persisted for at least 30 years in the soil. Mean small burnet seed density was 24 seeds/mÂ²; mean burial depth was 4 inches (10 cm) (review by ). In greenhouse studies in Italy, small burnet germinants showed 63% frequency in soil samples collected from grassland. In soil samples collected on former grassland sites converted to cedar (Cedrus deodora, C. atlantica) plantations 26 years before the study, small burnet germinants had 20% and 40% frequency in soils collected from plantations with respectively "sparse" and "dense" cedar plantings .
Small burnet seed stored in a warehouse for 25 years showed no appreciable drop in germinability, raising the possibility of a long-lived seedbank on some sites. Mean seed viability after 2 years was 88%; viability was still 88% after 15 years and 83% after 25 years of storage [125,126]. Humid conditions reduce the viability of soil-stored small burnet seed .
Germination and emergence: Germination rate of commercial small burnet seed is "excellent" . Germination rates of 90% to 95% have consistently been obtained in Great Basin wildlands [58,82,120]. Small burnet seed from a commercial mixture showed 90% germination in field trials near Silver Lake, Oregon. Study plots were in a western juniper (Juniperus occidentalis) community (review by ).
Seeds require an afterripening period before germinating [58,106]. In the laboratory, 80% of small burnet seed germinated within 21 days of sowing, and 91% of the seed had germinated 35 days after sowing . Warehouse-stored seed showed improved germination rates each year through 3 years of dry storage . Information on small burnet seed viability and emergence rates for naturally-reproducing North American populations were not available as of 2008. Naturally reproducing small burnet populations in Spain showed 50% emergence in the field (Salmeron 1966, cited in ).
The paired seeds in small burnet's hypanthium emerge within 1 to 4 days of one another, with the earliest emergent usually dominating . In the greenhouse, commercial small burnet seed from Oregon showed 54% emergence. Plants germinating from large seeds had higher mean stem and root lengths, more massive roots, and larger leaf areas than plants from small seeds (P<0.05) . Highest seedling emergence occurs when small burnet hypanthia are lightly covered with soil no more than 0.25 inch (6 cm) deep . Soil texture may affect emergence rate. In field studies in New Zealand, small burnet seed from Oregon showed 62.2% emergence in sand and 26.5% emergence in silty loam .
Seedling establishment/growth: North American populations of small burnet grow well on arid rangelands . Because of deliberate selection and breeding, North American populations often have greater seedling survivorship and "vigor" and are more productive than small burnet populations in the Old World [25,81,117]. Small burnet establishes easily from commercial seed, usually providing "good ground cover" within 1 or 2 years of seeding . Small burnet seedlings grow taproots "rapidly" , providing access to moist, lower soils layers early in development. Its overall growth is rated as "rapid" and "good to excellent" in sagebrush, pinyon-juniper, and mountain brushland zones [83,120,156].
Small burnet stands may be self-sustaining in the Great Basin, provided they are protected from grazing enough to set seed every 3 or 4 years . Small burnet in New Zealand reseeded naturally after domestic sheep and rabbits were excluded .
Vegetative regeneration: Small burnet sprouts from the caudex [79,117]. Some plants also sprout from rhizomes [109,115,116,119], but rhizomes are short [116,119], so clonal expansion of small burnet is limited .