Glandular and non-glandular hairs in the winter and summer leaves of the seasonally dimorphic Teucrium polium (Lamiaceae)

Teucrium polium is a seasonally dimorphic plant having short shoots and leaves in winter and long shoots and leaves in summer. Both the winter and summer leaves are covered with an indumentum of glandular and non-glandular hairs. Winter leaves bear more numerous hairs compared to summer leaves. Glandular hairs comprise peltate and capitate hairs. Peltate hairs consist of a unicellular epidermal foot, an also unicellular stalk, and a 4-celled head. Capitate hairs are of two sorts, long and short. Long hairs are composed of a unicellular epidermal foot, a 3-celled stalk, and a unicellular head, while short hairs of a unicellular foot, a unicellular stalk, and a 2-celled head. Histochemical tests showed that peltate hairs secrete essential oil and capitate hairs mucilage. Non-glandular hairs are mostly dendroid multicellular, but uniseriate multicellular hairs also exist. Both glandular and non- glandular hairs are implicated in chemical and mechanical defence against winter cold stress.