MEDICAL BOTANY - A.G. Serbin - 2003

SECTION 3. SYSTEMATICS

SUPERKINGDOM EUCARYOTA. KINGDOM PLANTAE

SPORE-PRODUCING PLANTS

DIVISION SPHENOPHYTA (EQUISETOPHYTA)

Horsetails constitute a single Class, EQUISETOPSIDA, in which only one order, EQUISETALES, has survived out of three. It is represented by a single family, Equisetaceae, and a single genus, Equisetum, uniting 15 species. Horsetails are most widely distributed in the Northern Hemisphere. They exhibit features of both hydrophytes and xerophytes and are highly polymorphic. The developmental cycle of Sphenophytes is shown in Fig. 3.104.

Fig. 3.104. Developmental cycle of field horsetail: A — spore-bearing SHOOT; B — vegetative shoot; C — female gametophyte; D — male gametophyte; 1 — rhizome with tubers; 2 — stem; 3 — lateral branches; 4 — leaf whorls; 5 — strobilus (spore-bearing cone); 6 — sporangiophore; 7 — sporangia; 8 — spores with elaters; 9 — germinating spores

The dominant generation is the sporophyte. These are perennial herbs with a rhizome, adventitious roots, and often tubers. The shoots branch monopodially and are termed articulate, as nodes and internodes are clearly defined. Shoots are either uniform — green, vegetative-reproductive, or of two types (dimorphic) — spring chlorophyll-free spore-bearing shoots, and summer vegetative, green, sterile ones. The internodes of the stems are furrowed-ribbed, hollow, mineralized with silica, brittle, and easily break into segments. Lateral branches are arranged in whorls. Leaves are reduced to scales collected into whorls that fuse into tooth-like sheaths enclosing the stem. Plants are homosporous, as the spores are morphologically identical, though they sometimes differ physiologically into (+) and (—), giving rise to dioecious prothallia. The spores bear ribbon-like outgrowths, or elaters, capable of spiral coiling and uncoiling depending on environmental humidity. This ensures that spores cluster together, allowing female and male specimens to germinate in close proximity, which facilitates Fertilization. Sporangia with spores are borne on sporangiophores, which are arranged in whorls, forming spore-bearing zones or terminal strobili on the shoot.

The reduced generation, the gametophyte, consists of monoecious or dioecious, short-lived, very small, green, thalloid plantlets. Spermatozoids are multiflagellate. The zygote lacks a resting period.

Certain horsetail species are used as medicinal raw Materials, while others are used for dyeing wool greyish-yellow. The dried, rigid stems of summer shoots are employed for cleaning dishes and polishing wooden, bone, and metal items. Starch-rich tubers, as well as young spore-bearing shoots of certain horsetails, are edible. However, some species are toxic to humans and animals (marsh horsetail, wood horsetail, and Water horsetail).

Class Equisetopsida

Family Equisetaceae

Field horsetail — Equisetum arvense (Fig. 3.104). Distributed in the temperate zone, it occurs in crops, meadows, and along the banks of water bodies. It is a perennial plant with a brownish-black rhizome and spherical tubers. The spore-bearing shoots, which appear in early spring, are 4 — 40 cm long, pinkish-brown, succulent, usually unbranched, articulate, and terminate in an ovoid-cylindrical strobilus. Leaf sheaths are tubular, dark brown, with 8 — 12 dark brown Teeth that often fuse in pairs at the tips. After spore maturation and dispersal, the spring shoots wither, and sterile summer vegetative shoots grow from the rhizome in their place. Their stems are 15 — 50 cm long, annual, light green, articulate, 4 — 5-angled, with a wide central cavity, and bear whorls of unbranched branches. Leaf sheaths are cylindrical and green; teeth are triangular-lanceolate with a dark margin, usually fused or adhering in groups of 2 — 3 at the tips. Lateral branches feature sharp Ribs and deep furrows; leaf sheaths are cylindrical, tightly appressed to the branch, with 4 — 5 long, narrow, acute teeth bent outwards.

In medicine, vegetative shoots are used as a diuretic, hemostatic, wound-healing, antiseptic, antihelminthic, and expectorant agent.