The seeds of Loasaceae subfam. Loasoideae (Cornales) I: Seed release, seed numbers and fatty acid composition

Seed release mechanisms, seed production, seed weights, and fatty acid composition are investigated for Loasaceae subfam. Loasoideae. A total of ca. 60 species are studied. Nearly all species have erect, xerochasious capsules which restrict the release of the (balistochorous and/or anemochorous) seeds to dry, windy conditions. Very few taxa have tardily dehiscent capsules that are dispersed as a unit (anemochoria, epizoochoria, Blumenbachia sect. Blumenbachia, Klaprothia mentzelioides) or one-seeded cypselas (anemochoria, Kissenia). Dehiscent, but non-xerochasious capsules are only found in Blumenbachia, and Blumenbachia sylvestis (B. sect. Angulatae) has seeds with good floating ability and may be occasionally hydrochorous. The seeds of all other Loasoideae taxa tested rapidly sink when placed in water. Seed weights range from less than 0.02 g per 1000 seeds (Huidobria, Presliophytum) to over 23 g per 1000 seeds (Loasa ser. Macrospermae), thus spanning 3 orders of magnitude. Seed weight seems to correlate to some degree with substrate and seeds are heavier in species from “deep substrates” such as gravel and leaf litter. Seed numbers per fruit range from 1 (Kissenia) to over 3000 (Presliophytum) and annual seed production of individual mature plants ranges from less than 100 (Kissenia) to over 4 ×10⁶ (Presliophytum). Fatty acid composition of Loasoideae seeds is mostly of common fatty acids, but exact composition varies considerably between groups. Most taxa have high levels of poly-unsaturated fatty acids (over 40% in Caiophora and Nasa), very low levels (<2%) are only found in Presliophytum. Nasa is the only genus of Loasaceae which has γ-linolenic acid and stearidonic acid in its seeds (at levels of 3.5–10% and 2–8.5% respectively). There is no obvious connection between the degree of unsaturation of the seed oils and habitat.