The Collaborative International Dictionary of English v.0.48:

Glasswort \Glass"wort`\, n. (Bot.)
   A seashore plant of the Spinach family (Salicornia
   herbacea), with succulent jointed stems; also, a prickly
   plant of the same family (Salsola Kali), both formerly
   burned for the sake of the ashes, which yield soda for making
   glass and soap.
   [1913 Webster]

WordNet (r) 3.0 (2006):

glasswort
    n 1: bushy plant of Old World salt marshes and sea beaches
         having prickly leaves; burned to produce a crude soda ash
         [syn: saltwort, barilla, glasswort, kali,
         kelpwort, Salsola kali, Salsola soda]
    2: fleshy maritime plant having fleshy stems with rudimentary
       scalelike leaves and small spikes of minute flowers; formerly
       used in making glass [syn: glasswort, samphire,
       Salicornia europaea]