Taxonomy & Evolution

Spreading the risk over time – Dormancy in trimorphic achenes of a cold desert annual

Do variations in dormancy and germination across achenes from peripheral, intermediate and central positions contribute to the success of the cold desert annual Heteracia szovitsii?

In botany, diaspore heteromorphism is a phenomenon in which fruits/seeds differing in morphology and/or ecological responses are produced by an individual plant. This allows the plant to spread the risk of plant establishment over time. Diaspore heteromorphism has been described in ~300 species in 26 families of flowering plants and is an adaptive strategy allowing species to persist in highly variable habitats. The diaspores may differ in size, shape, colour and mass, as well as in ecological attributes such as dispersal and dormancy/germination characteristics. Many studies have investigated the ecology of species with dimorphic diaspores, yet relatively little is known about species with trimorphic diaspores.

Morphological characteristics of the three achene morphs of Heteracia szovitsii. (A, B) Peripheral achene morph (A, abaxial side; B, adaxial side); (C) intermediate achene morph; (D) central achene morph. Image credit: Lu et al.

In their new study published in AoBP, Lu et al. investigated diaspore dormancy of Heteracia szovitsii (Asteraceae), an annual species of the cold deserts of China that produces three achene morphs in each inflorescence. The authors tested the dormancy breaking/germination responses of the three achene morphs and of seeds isolated from the pericarp in the laboratory using standard procedures. Seedling emergence phenology of the achene morphs was monitored under natural cold desert temperature conditions in an experimental garden. H. szovitsii exhibited a temporal dispersal strategy, with central achene morphs emerged over a period of 12 months after sowing, while intermediate and peripheral achene morphs did so for 40 and 47 months, respectively. These results were combined with data from a previous study of diaspore dispersal of this species, with the authors concluding that H. szovitsii has a high-intermediate-low risk diaspore dispersal/dormancy strategy. This likely increases the chances for population persistence over time and space in cold desert habitats in Central Asia.

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