BOTANY WITH THE BASICS OF HYDROBOTANY (AQUATIC PLANTS OF UKRAINE) - B.Ye. Yakubenko - 2011

VIII. FUNDAMENTALS OF PLANT MORPHOLOGY AND ANATOMY

Morphology and Anatomy of the Leaf

Compound Leaves

Compound leaves also exhibit significant diversity. A compound leaf possesses two or more blade segments. While a simple leaf consists of a petiole and a single blade and is shed entirely as a single unit, a compound leaf features a rachis (a common axis) along with multiple leaflets, each with its own petiole, allowing individual leaflets to detach separately (Fig. 74).

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Fig. 74. Schemes for morphological leaf analysis (after P.M. Potulnytskyi)

Depending on the arrangement of leaflets along the rachis, compound leaves are classified into several types: trifoliate, consisting of 3 leaflets on short petioles (such as clover), as well as pinnately and palmately compound leaves. Pinnately compound leaves are further subdivided into paripinnate, where simple leaflets are paired along the common axis, and imparipinnate, in which the leaf terminates in a single terminal leaflet while the remaining leaflets are arranged in pairs. Leaves may also be bipinnate or tripinnate (Fig. 75).

Fig. 75. Shapes of simple leaves based on blade dissection:

a - trilobed, b - trifid, c - trisect, d - palmatilobed, e - palmatipartite, f - palmatisect, g - pinnatilobed, h - pinnatipartite, i - pinnatisect

Leaves vary considerably in size. In some plants, their length ranges from a few millimeters (duckweed) up to 22 m (palms). In the majority of plants, however, they do not exceed 2-5 cm, and rarely 10-15 cm.

Phyllotaxy (Leaf Arrangement). To make more efficient use of solar energy, leaves attach to the stem in various ways, acquiring different spatial orientations. The most common types of phyllotaxy are alternate, opposite, and whorled. Another recognized type is mosaic phyllotaxy, in which leaves are arranged in a single plane without shading one another, thanks to varying petiole lengths (Fig. 76).