The Collaborative International Dictionary of English v.0.48:

Portulaca \Por`tu*la"ca\, n. [L., purslane.] (Bot.)
   A genus of polypetalous plants; also, any plant of the genus.
   [1913 Webster]

   Note: Portulaca oleracea is the common purslane. Portulaca
         grandiflora is a South American herb, widely
         cultivated for its showy crimson, scarlet, yellow, or
         white, ephemeral blossoms.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Purslane \Purs"lane\, n. [OF. porcelaine, pourcelaine (cf. It.
   porcellana), corrupted fr. L. porcilaca for portulaca.]
   (Bot.)
   An annual plant (Portulaca oleracea), with fleshy,
   succulent, obovate leaves, sometimes used as a pot herb and
   for salads, garnishing, and pickling.
   [1913 Webster]

   Flowering purslane, or Great flowered purslane, the
      Portulaca grandiflora. See Portulaca.

   Purslane tree, a South African shrub (Portulacaria Afra)
      with many small opposite fleshy obovate leaves.

   Sea purslane, a seashore plant (Arenaria peploides) with
      crowded opposite fleshy leaves.

   Water purslane, an aquatic plant (Ludwiqia palustris) but
      slightly resembling purslane.
      [1913 Webster]

WordNet (r) 3.0 (2006):

Portulaca oleracea
    n 1: weedy trailing mat-forming herb with bright yellow flowers
         cultivated for its edible mildly acid leaves eaten raw or
         cooked especially in Indian and Greek and Middle Eastern
         cuisine; cosmopolitan [syn: common purslane, pussley,
         pussly, verdolagas, Portulaca oleracea]