Halophytes

Halophytes are a special group of plants adapted to grow in soils with a high concentration of dissolved salts, typically found near sea-shores and in estuaries, where the vegetation as a whole is known as mangrove forest and the individual plants as mangroves. The defining physiological puzzle for a halophyte is that its soil is physically wet (there is plenty of water around) but physiologically dry (the plant cannot use salt water directly and must actively filter salt out through dedicated physiological processes before the water becomes usable). Morphologically, temperate halophytes tend to be herbaceous while tropical halophytes are mostly bushy/woody; in addition to their normal root system, many mangroves grow extra stilt roots for support in soft, unstable mud, along with specialised negatively geotropic (upward-growing) roots called pneumatophores, dotted with pores called pneumathodes that let air reach the submerged root system below — these are commonly called breathing roots (e.g. in Avicennia). Halophyte leaves are typically thick, entire (undivided), succulent and glossy, and are coated with a thick cuticle on all aerial parts; some species are even aphyllous (leafless) altogether, carrying out photosynthesis in green stem tissue instead. A distinctive reproductive adaptation seen in many mangroves is vivipary, where the seed germinates while still attached to the parent plant, giving the seedling a head start before it ever drops into the mud below. Anatomically, the epidermal cells of a halophyte's stem are heavily cutinised, almost square in shape, and packed with oil and tannins; 'star'-shaped sclereids and 'H'-shaped heavily thickened spicules reinforce the cortex mechanically; and the leaves may be dorsiventral or isobilateral, equi …