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

VIII. BASICS OF PLANT MORPHOLOGY AND ANATOMY

Morphology and Anatomy of the Leaf

Types of Leaves

Simple and compound leaves are distinguished.

Simple leaves are those consisting of a single leaf blade and a petiole. At the end of the growing season, the leaf falls off entirely, separating from the stem.

Compound leaves are those in which individual simple leaflets are borne on a common petiole. The latter leaflets vary greatly in shape and fall off individually.

Simple leaves. When describing a leaf blade, such features as its shape, length-to-width ratio, degree of lobing, and margin outline are used.

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Fig. 73. Shapes of simple leaves:

1 - linear, 2 - lanceolate, 3 - elliptic, 4 - ovate,

5 - obversely broadly cordate, 6 - broadly cordate,

7 - reniform, 8 - peltate, 9 - orbicular, 10 - lobed,

11 - sagittate, 12 - hastate, 13 — acicular

Depending on the shape of the leaf blade, the following simple leaves are distinguished (Fig. 73):

- linear - a narrow, elongated leaf blade many times longer than its width, featuring a long sheath and a ligule at the junction with the blade (grasses);

- lanceolate - the width of the leaf base is nearly four times less than its length (some willow species, clubmoss, oleander);

- oblanceolate - the width of the leaf apex is nearly three to four times less than its length (ox-eye daisy);

- orbicular - the length of the leaf blade is nearly equal to its width (aspen, nasturtium, wintergreen);

- elliptic - simple leaves whose blade is rounded and approaches the shape of a regular ellipse (blueberry, lingonberry);

- ovate - the width of the leaf blade base is nearly twice less than its length (lilac, hornbeam, plantain);

- obovate - the width of the leaf apex is 1.5–2 times less than its length (barberry, alder, Chinese poplar);

- broadly ovate - the width of the leaf blade base is nearly equal to its length (apple, lilac);

- broadly obovate - the width of the leaf blade apex is nearly equal to its length (hazel);

- oval - the length of the leaf blade is nearly twice greater than its width (pear, bird cherry);

- linear — the length of the leaf blade is more than three times its width (e.g., in bindweed);

- ensiform (sword-shaped) — the length of the leaf blade significantly exceeds its width (iris);

- cordate — the Base of the leaf blade is Heart-shaped, and the apex is pointed (buckwheat, violet, linden, ivy);

- reniform (Kidney-shaped) — a leaf with a kidney-shaped base of the leaf blade and a blunt apex (ground ivy, wild ginger);

- rhombic — the base of the leaf blade is cuneate (black poplar — aspen);

- hastate — the base of the leaf blade is spear-shaped (field bindweed, sheep's sorrel);

- sagittate — the base of the leaf blade features a deep triangular notch (arrowhead);

- triangular — the base of the leaf blade is triangular (orache);

- acicular (needle-shaped) — simple leaves whose leaf blade shape resembles a needle (pine, spruce);

- spathulate — a simple leaf with a rounded, oval, or oblong leaf blade that transitions into a broad petiole (bugleweed).

According to the margin of the leaf blade, leaves can be: entire (lilac, plantain, rye, oak, lily of the valley); sinuate — margins have alternating notches of various shapes (coltsfoot, aspen, orache); dentate — the leaf margin ends in sharp Teeth (hazel, nettle); serrate — with teeth directed toward one apex (pear, linden, willow, violets, mulberry); crenate — with rounded teeth at the apex (ground ivy), etc. (Fig. 74).

The apex of the leaf can be obtuse, acute, acuminate, cuspidate, etc. (Fig. 76).

The shape of the leaf blade base can be: rounded, narrowed, cordate, sagittate, etc. (Fig. 74).

According to the degree of dissection of the leaf blade, leaves are classified as:

- entire — having an undissected blade (lilac, birch);

- incised — having notches less than % of the leaf blade;

- lobed — notches do not exceed 1/4 of the width of the leaf half-blade: trilobed (hop), pinnately lobed (oak), palmately lobed (field maple);

- cleft — notches are deeper than 1/4 of the width of the leaf half-blade: pinnately cleft (dandelion), palmately cleft (Norway maple);

- partite — notches reach halfway across the width of the leaf blade, i.e., reaching the midrib: tripartite (creeping buttercup), pinnately partite (celandine, tomatoes), palmately partite (bulbous buttercup, some geranium species).

The protruding parts in lobed leaves are called lobes, in cleft leaves — divisions, and in partite leaves — segments.

If a pinnately partite leaf has large divisions alternating with small ones, it is called interruptedly pinnately partite (potato). Sometimes blades are dissected twice or multiple times (yarrow, dill, carrot).

Lyrate leaves — pinnately partite leaves with a terminal rounded elongated lobe much larger than the lateral ones, and small blunt triangular lateral lobes (celandine, avens, radish, yellow rocket). Runcinate leaves — pinnately partite or pinnately dissected, with triangular lobes or blade segments having a widened base (dandelion).

Venation. The leaf is permeated by a mass of vascular bundles or their elements (Veins), which ensure the influx of water and mineral salts, as well as the outflow of plastic substances. Together, they form a specific leaf venation pattern. It can be dichotomous, parallel, campylodromous (arcuate), and pinnate, which is subdivided into palmate and reticulate.

Parallel, or linear, and arcuate venation is characteristic of monocots and is distinguished by veins running parallel from the base to the apex (cereals) or diverging in an arcuate manner from the base (lily of the valley).

Reticulate venation is characteristic of dicotyledonous plants. The veins are extensively branched and form a net-like appearance (grape, bean), hence its name.