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Hypericum species are quite variable in habit, occurring as trees, shrubs, annuals, and perennials. Trees in the sense of single stemmed woody plants are rare, as most woody species have multiple stems arising from a single base. Shrubs have erect or spreading stems but never root from nodes that touch the ground. However, perennial herbs tend to root from these horizontal nodes, especially those that occur in wet habitats. Annual herbs tend to have taproots with a developed system of secondary hair roots. Many species of Hypericum are completely glabrous, others have simple uniseriate hairs, and some species have long, fine hairs.
Two types of glands form the characteristic punctiform patterns of Hypericum, "dark glands" and "pale glands". Dark glands consist of clusters of cells with a distinct black to reddish color. Their hue is indicative of a presence of naphthodianthrone, either hypericin or pseudohypericin, or both. These glands occur in about two-thirds of Hypericum sections and are usually restricted to certain organs. When these glands are crushed, the naphthodianthrones give a red stain. Paracelsus called the red secretions "Johannes-blut" in the 16th century, linking the plant to the martyr St. John and giving rise to the English and German common names of "St. John's wort". The pale glands, forming the pellucid dots, are each a schizogenous intracellular space lined with flattened cells that secrete oils and phloroglucinol derivates, including hyperforin. The distribution of these hypericin glands dissuades generalist herbivores from feeding on the plants. When generalist insects feed on Hypericum perforatum, 30-100% more naphthodianthrones are produced, repelling the insects.
The four thin ridges of tissue along the stems are closely to the opposite-decussate leaves of Hypericum. The ridges can be minor, just being called "ridges", or prominent, being called "wings". Terete, two-lined, and six-lined stems can occur occasionally. When a species has a tree or shrub habit, the internodes become mostly terete with age, though some trace of lines can still be detected in mature plants. The number of lines is an important distinguishing characteristic; for example, H. perforatum and Hypericum maculatum are easily confused save for H. perforatum having two lines and H. maculatum having four. The pale and dark glands are present on stems of various species, and other various species have stems without any glands. In section Hypericum, the glands are only present on stem lines, and in other sections, including Origanifolia and Hirtella, the glands are distributed across the stems.Hypericum flowers have four or five fascicles that have, in total, five to two hundred stamens. The fascicles can be free or fused in various ways, often into three apparent fascicles. In sections Myriandra, Brathys, and some of Trigynobrathys, the stamens form a ring. Though stamens are usually persistent, some are deciduous. The stamens have an anther gland on the connective tissue, varying in color from amber to black. (Source: en.wikipedia.org)