Portulaca
2 of the 7 encyclopedias on this shelf carry an entry for Portulaca. Both are reproduced below, so you can see where they agree and where they differ.
Aiton's Encyclopedia (1910)
a genus of plants, so named by the botanist Tournefort. There are about twenty species, chiefly tropical. All are fleshy herbs, prostrate or ascending, with thick juicy leaves. The ovary is one-celled and contains a mass of small, shiny seeds. The garden portulaca has showy terminal flowers, red, yellow, purple, and variegated. They open in bright sunshine and close on the approach of a shower or at eventide. The common purslane is known to botanists as Portulaca oleracea. It is a common weed in American gardens. It is capable of resisting drouth, and, even when cut off by the hoe, it will root again if left on moist earth. The flowers of this species are inconspicuous. Other members of the portulaca family are the Claytonia, or spring beauty, and the bitter root, or Lewisia, of the Rocky Mountains . A related shrub of Cape Colony is known as the purslane tree. Related species from California, Peru, and Australia are known to the horticulturist as Calandrinia.
Collier's New Encyclopedia (1921)
purslane; the typical genus of the Portulacaceæ; low, succulent herbs with flat or cylindrical leaves, and yellow, purplish, or rose-colored ephemeral flowers. Known species between 30 and 40; most of them from the warmer parts of America. P. oleracea is the common purslane. It is a low, succulent annual, often eaten by the Hindus as a potherb. P. quadrifida, also Indian, is eaten and considered cooling by the natives. The fresh leaves of both species are used as an external application in erysipelas, etc., and an infusion of them as a diuretic. PORTULACACEÆ or PORTULA- CEE, purslanes; an order of hypogynous exogens, alliance Silenales. Succulent herbs or shrubs, generally with alternate, entire leaves; axillary or terminal flowers, which expand only in bright sunshine. Sepals two; petals five, distinct, or joined into a tube; stamens varying in number; carpels three or more; ovary and capsule one-celled, the latter dehiscing transversely, or by valves (Lindley). Known genera 15, species 125 (Sir Joseph Hooker).