This section is from the book "British Wild Flowers In The Four Seasons", by Thomas Moore. Also available from Amazon: British Wild Flowers.
* Calyx-teeth not longer than the tube.
G. Ladanum: annual; stems 6-8 inches high, with spreading, almost decumbent branches, covered with short soft down, not swollen under the nodes; leaves narrow-ovate or lanceolate, coarsely toothed; flowers purple, in dense whorls in the upper axils, the upper ones forming a terminal head. - Cultivated and waste places. Fl. August, September.
** Calyx-teeth long and almost prickly.
G. Tetrahit: annual; stems coarse, 1-2 feet high, swollen under the nodes, with spreading branches, and stiff, spreading hairs; leaves ovate, pointed, coarsely toothed; flowers numerous, forming close whorls in the axils of the upper leaves, pale-purplish or white. - Cultivated and waste places. - Fl. July, August.
Var. versicolor, larger, with larger flowers, which are yellow with a purple spot on the lower lip. - Fields.
 
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