Knotted Pearlwort

Foodplant / parasite
hypophyllous telium of Puccinia arenariae parasitises live leaf of Sagina nodosa

Knotted pearlwort has a unique way of reproducing. Besides producing seeds, it also makes bundles of leaves which break off in the autumn. These bundles are carried by water or wind to other suitable areas where they take root. In this way, the plant skips the risky stage of germination. Although found throughout the Netherlands, knotted pearlwort is not common. It grows mostly on open, damp areas, such as beach plains, young dune slacks and peaty soils. Knotted pearlwort is found in cold and mild climates in coastal regions in the northern hemisphere.

Plants perennial, tufted, pubescent or glabrous. Stems ascending to loosely spreading or prostrate, simple or with few to many lateral branches bearing only tiny, succulent, subulate leaves, not filiform. Leaves: axillary fascicles of subulate, fleshy leaves among distal cauline leaves, giving knotted appearance; basal ascending, forming tuft, not in rosettes, blade linear, ca. 15-30 mm, herbaceous, apex apiculate to mucronate, glabrous or glandular; cauline conspicuously connate basally, cuplike, proximal with blade linear to subulate, apex apiculate to mucronate, glabrous or glandular-pubescent, axillary fascicles of leaves absent; distal with blade subulate, 1-1.5 mm, fleshy, apex mucronate, glabrous. Pedicels filiform, base glabrous or glandular-pubescent. Flowers terminal and axillary, 5-merous or 4- and 5-merous; calyx base glabrous or glandular-pubescent; sepals elliptic, 2-3 mm, hyaline margins rarely purplish, apex frequently purplish, obtuse to rounded, remaining appressed after capsule dehiscence; petals elliptic to orbiculate, 3-4.5 mm, ca. 2 times sepal length; stamens 8 or 10. Capsules 3-4 mm, longer than sepals, dehiscing to base. Seeds dark brown, ovoid to reniform, laterally compressed, 0.5 mm, smooth or distinctly pebbled, abaxial groove present or absent.

Subspecies 2 (2 in the flora): North America, Europe.

Spergula nodosa Linnaeus, Sp. Pl. 1: 440. 1753

Sagina nodosa, the knotted pearlwort, is a species in the genus Sagina, native to northern Europe. It is a low-growing plant up to 15 cm tall, with paired leaves up to 1 cm long. The flowers are 5–10 mm diameter, with five white petals.