2. Geranium L. (crane’s bill) (Aedo, 2000, 2001)

Plants annual, biennial, or perennial herbs, sometimes with rhizomes. Stems prostrate to erect or ascending at maturity, sometimes reddish- or purplish-tinged. Leaves basal and alternate or opposite. Leaf blades simple, shallowly to deeply palmately lobed with mostly 5–9 main lobes, the main veins palmate, the veins and margins sometimes reddish- or purplish-tinged. Stipules mostly 3 at each node (by fusion of adjacent stipules on 1 side but not the other). Inflorescences axillary clusters of mostly 2–5 flowers, usually appearing umbellate. Sepals narrowed or tapered (sometimes abruptly so) to a minute sharp point or short awnlike extension at the tip. Stamens 10 (5 in G. pusillum), the filaments free or fused at the base, gradually broadened toward the base. Staminodes absent (5 in G. pusillum, these scalelike, shorter than the filaments of fertile stamens). Mericarps at maturity with the stylar beaks remaining attached to the apical portion of the column, the basal portion ovoid (rounded or broadly angled at the base), curling upward, dehiscent. Seeds oblong-ellipsoid, the surface smooth or with a fine network of ridges and pits, brown. Three hundred to 430 species, nearly worldwide, but most diverse in temperate regions.

Seed dispersal in most Geranium species is explosive. As the mature fruit dries, the beak of each mericarp acts as a spring, placing outward tension on the basal portion. At dehiscence, the apical portion of the beak remains fused to the central column and the basal, seed-containing portion is suddenly released, curling upward, catapulting the seed up to several hundred cm away (K. R. Robertson, 1972).

In some species, the stylar beak is differentiated into 2 regions, a longer columnar portion above the seed-containing base, which is tapered abruptly into a slender beaklike extension above the column and below the stigmas, but in other species this extension is absent and the columnar portion narrows directly into the stigmatic region. This distinction is perhaps confusing when rendered into words, but is an important character in the determination of fruiting specimens.