This section is from the book "Handbook Of Hardy Trees, Shrubs, And Herbaceous Plants", by W. Botting Hemsley. Also available from Amazon: Handbook of hardy trees, shrubs, and herbaceous plants.
Herbaceous or suffruticose plants having terete stems and alternate simple exstipulate usually scabrid leaves. Flowers regular or irregular, in gyrate spikes, racemes or cymes, rarely solitary and axillary. Calyx persistent, 4- or 5-lobed, valvate in bud. Corolla of various forms, usually 5-lobed, with an imbricate aestivation, the throat often furnished with hairs or scales opposite the lobes. Stamens equalling the corolla-lobes in number and alternate with them. Fruit of 4 indehiscent 1-seeded distinct nuts, or rarely of two 2-celled nuts; seeds separable from the pericarp, usually destitute of albumen. This is an extensive order, comprising 50 genera and 600 species, distributed all over the globe, and especially abundant in the Mediterranean region.