Silique valves as sails in anemochory of Lunaria (Brassicaceae)

Abstract

The generally held opinion that seeds of Lunaria remain at the replum after detachment of the two valves and then wind causes a shaking or rattling of the replum with its diaphragm, thus launching the seeds, is challenged. In a sparse forest in the Swabian Alb, the first author noticed flying valves of Lunaria rediviva to which the narrow-winged flat seeds are attached. Investigations with SEM and histology have shown that the valves secrete a glue only at those sites where the seeds rest on the valves before valve tissues die. Further analysis has shown (using the periodic acid-Schiff reaction) that the glue consists of polysaccharides. After detachment and dispersal of the valves, the adhesive strength continuously decreases. This is the first report for a sticky valve exudate in the Brassicaceae. Because of the adhesion of Lunaria seeds to their valves for some time, the 1st order diaspore is a mericarp, in a broad sense, and can be interpreted as an adaptation to long-distance dispersal by stronger winds. In this context, the 'flying carpets' of Lunaria are more effective and transport more than one seed. Molecular studies assigned Lunaria to the tribe Biscutelleae, which now contains the angustiseptate genera Biscutella and Megadenia as well as the latiseptate genera Lunaria and Ricotia. The valves in Ricotia can easily be detached (studied in herbarium material and a living plant), but, in contrast to Lunaria, the ripe seeds remain at the replum and its diaphragm, respectively.

Seed mucilage evolution: Diverse molecular mechanisms generate versatile ecological functions for particular environments

“…The combination of both traits can provide a powerful dispersal advantage until an optimal place regarding hydric conditions is reached (Figure 5a-2). Interestingly, Lunaria annua shows a surprising use of mucilage by secreting it from the inner surface of the fruit, keeping the four seeds attached, even after its dehiscence, this allows a differential dispersion between the two halves of the fruit and their two attached seeds by the wind (Leins, Fligge, & Erbar, 2018).…”

Photonic paper: Multiscale assembly of reflective cellulose sheets in Lunaria annua

“…In the Lunaria genus, the fruit shape is believed to have been optimized by the plant to promote anemochorous seed dispersal, hence the light, large, and flat elliptical shape of the valves and, possibly incidentally, of the septum ( 22 , 24 , 26 ). During growth, the seeds attach to the valves so that when the mature fruit opens due to the accumulated tension in the valves, the valves detach from the replum and disperse the glued seeds via anemochory ( 26 – 28 ). On the contrary, the septum remains on the plant, displaying a notably shiny appearance that justifies Lunaria ’s popular use as ornamental plant.…”

“…1, A and B). The Lunaria seedpods consist of a dehiscent capsule of three flat elliptical membranes, as typical of the genus Lunaria (25,26): the two external matte valves create a silicle for the development of the seeds, which originate from the internal silvery-white partitioning false septum (Fig. 1A).…”

Seed mucilage evolution: diverse molecular mechanisms generate versatile ecological functions for particular environments

“…Combination of both traits can give a powerful advantage by an efficient dispersal until an optimal place for hydric conditions is reached (Figure 5A-2). Interestingly, Lunaria annua shows a surprising use of mucilage by secreting it from the inner surface of the fruit to keep the four seeds sticked to it, even after its dehiscence, allowing a differential dispersion between the two halves of the fruit and their two attached seeds by the wind (Leins, Fligge & Erbar 2018).…”