Lessons 43–44 · 2 lessons · O. Pratov, A. Tukhtaev, F. Azimova, I. Saparboev, M. Umaraliyeva. Biology (Botany), Grade 6. O‘zbekiston Publishing House, Tashkent, 2017
43
Division Horsetails
Textbook: pp. 103–104
GoalExplain the structure, reproduction and importance of horsetails (field horsetail, Equisetum arvense).
Horsetails are perennial herbs that grow in damp places along ditches, canals, drains and springs. The stem of the field horsetail is ribbed and divided into joints, with hollow internodes; thin branches and tiny scale-like leaves sit in rings only at the joints, which gives the plant its name. In early spring buds on the rhizome send up a brown, unbranched spring shoot; at its tip is a cone with rings of sporophylls, and 6–8 sporangia ripen under each sporophyll. Spores are scattered by wind and water; on damp ground they grow into a small green gametophyte bearing antheridia and archegonia; fertilization takes place only in water, and the zygote grows into a new plant, the sporophyte. After the spring shoot withers, a green, branched summer shoot grows in early summer and photosynthesizes. Horsetail also spreads vegetatively by its rhizome. It is a medicinal plant (diuretic), but it should be used only on a doctor’s advice.
Early spring: a spring shoot grows from a rhizome bud→Spores ripen in the cone at its tip→Spores are spread by wind and water→A small green gametophyte grows on wet ground→Fertilisation in water; the zygote grows into a new plant (sporophyte)
Worked examples
Spring shoot: brown, unbranched, spore cone at the tip; summer shoot: green, branched, photosynthesizing.
Uzbekistan has 2 horsetail species: the field horsetail (with a spring shoot) and the many-branched horsetail (no spring shoot; cones at the tips of branched shoots).
Class activity
Observation: in spring and summer find shoots of the field horsetail, compare and draw them and make a herbarium sheet. Safety: stems are rough (they contain silica), so handle them carefully; do not taste or brew them; walk on damp slippery banks with adults; wash hands.
Practice
1
Why is the plant called a “horsetail” (qirqbo‘g‘im, “forty joints”)?
Its stem is jointed, with branches and leaves in rings at the joints.
2
Where do the spores ripen?
In the cone at the tip of the spring shoot, in sporangia under the sporophylls.
3
If every sporophyll has 6 sporangia, how many sporangia do 8 sporophylls have? (6 × 8)
48
4
Why is the summer shoot green but the spring shoot brown?
The summer shoot photosynthesizes (it has chlorophyll); the spring shoot only releases spores.