Abstract:

Aims Members of Brassicaceae are one of the most important groups of ephemeral plants in the Junggar Basin and serve many ecological roles in the desert. However, studies on dispersal syndromes of Brassicaceae, especially the ephemerals, are rare. This study addresses the following questions: 1) what are the dispersal unit and the dispersal mode of these species, 2) what are the spatio-temporal patterns of dispersal of these species and 3) how are these characters adaptive to the arid desert environment?

Methods The study was conducted on 24 ephemeral species of Brassicaceae from June to October 2005 and 2006. We observed and recorded 1) morphology of the fruits and seeds, 2) dehiscence mode of the fruit, type of dispersal unit and accessory structures and 3) dispersal mode and its duration in natural habitats.

Important findings The dehiscence mode of fruit depends on degree of lignification. There are three types of dispersal units of the species whose pods cannot dehisce. Species whose dispersal unit is the fruit node are autochorous. Species in which dispersal occurs by the whole fruit have silicula. Some do not have accessory structures to dispersal, and the dispersal mode is autochorous. Others have wings or hairs and disperse by wind. Species whose dispersal unit is a section of the infructescence also have silicula with a hard and hook-like beak that can attach to the coat of animals. Species with pods that dehisce easily only disperse by seeds. Their seeds have three types. One type is tiny without any accessory structures for dispersal, and seeds are dispersed by wind. Seeds in the second type have wings, and their modes of dispersal are diverse, but the main one is hydrochory. Seeds in the third type have wings and mucilage and are dispersed by anemochory and hydrochory. There are two types of dispersal patterns, depending on duration of dispersal. The first type is the short-term dispersal pattern in which all dispersal units on the plant are dispersed from the mother plant mainly in June and July. In the second type, dispersal units are shed from the mother plant from June to October or even the next spring. In this pattern, pods in the upper and lower positions of one infructescence differ in morphology, degree of lignification, kind of dispersal unit, dispersal time and dispersal mode.

Key words: dispersal syndromes, ecological adaptation, Brassicaceae, ephemerals, Junggar Desert