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Last Update 06/03/08

Botany 101

Leaves

Evergreen plants have foliage that remains functional through more than one growing season, whereas deciduous plants shed all or nearly all their foliage each year. A typical leaf consists of two principal parts: the expanded leaf blade or lamina, and the slender leaf stalk or petiole. Frequently there are scaly or leaf-like outgrowths at the base of the petiole known as stipules , which may be leaf-like, spines, or glands. In dicots and some gymnosperms, the lamina is a thin sheet of green tissue strengthened by the midrib and lateral veins. There are three main types of venation in leaves:

  1. In parallel - veined leaves, the veins run parallel to each other. This condition is characteristic of the monocotyledoneae. Parallel veins may run lengthwise on the leaf, as in Eucharis grandiflora (Amazon lily), or they may be parallel, but directed outward from the midrib to the margin (penniparallel).
  2. Pinnately - veined leaves have a single primary vein or midrib, from which smaller veins branch off, like the divisions of a feather. Examples are Eriobotrya japonica (loquat) and Camellia japonica (camellia).
  3. Palmately - veined leaves have several principal veins radiating from the base of the leaf blade, as in Acer rubrum (red maple) and Carica papaya (papaya).

 

Leaf Forms

Linear - narrow, several times longer than wide, and essentially of the same width throughout.

Lanceolate - much longer than wide and tapering towards the apex from a broader base.

Oblanceolate - much longer than wide, tapering towards the base instead of the apex (the opposite of lanceolate).

Oblong - nearly twice as long as broad, with the sides nearly or parallel most of their length.

Elliptic - oblong, broadest in the middle with the two ends narrowing.

Ovate - egg-shaped, with the broadest part near the base.

Obovate - opposite of ovate, with the narrower part near the base.

Cuneate - wedge-shaped, broad at the tip and tapering by nearly straight lines to an acute angle at the base.

Spatulate - oblong but tapering to a narrow base; spoon-shaped.

Sagittate - arrow-shaped; lobes at base acute and pointing downward, while the main body tapers upward to a point.

Leaf Bases

Cordate - heart-shaped.

Reniform - kidney-shaped; like cordate but rounder and broader than long.

Auriculate - a small pair of projections, or ears, usually at the base.

Hastate - halberd-shaped; lobes at base pointed and narrow and nearly at right angles to petiole.

Oblique - slanting, unequal-sided.

Leaf Tips

Acuminate - prolonged into a narrowed or tapering point.

Acute - ending in an acute angle, but not a prolonged point.

Obtuse - blunt or rounded apex.

Truncate - square end that looks cut off.

Emarginate - indented or notched.

Obcordate - inversely heart-shaped; an obovate leaf which is much more deeply notched at the tip.

Cuspidate - tipped with an elongated sharp or rigid point.

Mucronate - abruptly tipped with a small, short point; like a mere projection of the midrib.

Leaf Edges/Margins

Entire - even line, without teeth, notches, or lobes.

Serrate - cut into sharp, saw-like teeth pointing forward.

Dentate - toothed, teeth point outward instead of forward and are large.

Crenate - teeth are short and rounded; also called scalloped.

Undulate - margin of the leaf forms a wavy line, bending slightly inward and outward in succession.

Sinuate - like undulate, margin is very wavy (sinuous).

Incised - cut into sharp, deep, and irregular teeth or incisions.

Lobed - incisions do not extend deeper than halfway between the margin and the center of the blade and are rounded.

Cleft - incisions extend more than halfway between the margin and the center of the blade, and are sharper.

Deeply Lobed - incisions are even deeper, but not quite to the midrib or base of the blade.

Leaf Divisions

Simple - blade is of one piece, as in Camellia japonica . It may still be simple and be lobed or cleft, as in Hibiscus rosa-sinensis (hibiscus), Quercus shumardii (Shumard oak), and Acer rubrum (red maple).

Compound - blade is made up of a number of separate leaflets. The two principal types of compound leaves are pinnate and palmate:

  1. Pinnate - leaflets or pinnae are arranged on the sides of the main leaf stalk. Examples are Nephrolepsis exaltata 'Bostoniensis' (Boston sword fern), Roystonea regia (Cuban royal palm), and Zamia floridana (coontie).
    • Odd Pinnate - pinnate with an odd number of leaflets; has an end leaflet. Examples are Schinus terebinthifolius (Brazilian pepper), Wisteria sinensis (wisteria), Tecomaria capensis (Cape honeysuckle), and Koelreuteria elegans (golden-rain tree).
    • Even Pinnate - pinnate with an even number of leaflets; no end leaflet. Examples are Senna alata (candle bush) and Tamarindus indica (tamarind).
    • Bi-pinnate - leaflets are twice pinnate (the primary pinnae or leaflets are again divided into secondary leaflets), such as in Albizzia julibrissin (mimosa), Delonix regia (royal poinciana), Melia azedarach (chinaberry), and Jacaranda spp. (jacaranda).
  2. Palmate - the leaflets are attached directly to the end of the petiole and extend outward much like fingers in a palm. Examples are Schefflera actinophylla (Australian umbrella tree) and Parthenocissus quinquefolia (Virginia creeper).

Leaf Arrangements on Stem

Alternate - one leaf at each node, as in Hibiscus rosa-sinensis (hibiscus), Brunfelsia australis (yesterday-today-and-tomorrow), and Citrus spp. (citrus).

Opposite - two leaves at each node, always on opposite sides of the stem. Examples are Catharanthus roseus (periwinkle), Ixora coccinea (ixora), and Viburnum odoratissimum (sweet viburnum).

Whorled - more than two leaves at a node spaced around the stem, as in Nerium oleander (oleander) and Macadamia spp. (macadamia).

 

Leaf Attachments

Petiolate - petiole (leaf stalk) is present, examples are Hibiscus rosa-sinensis (hibiscus) and Quercus spp. (oaks).

Sessile - attached directly to the main stem or branch without a petiole, as in Podocarpus macrophyllus (Japanese yew) and Gloriosa superba 'Rothschildiana' (gloriosa lily).

Peltate - petiole attached to the lower surface of the leaf instead of at the base or margin, as in Tropaeolum majus (garden nasturtium).

Clasping - leaf partially encircles the stem, as in Calendula officinalis (calendula).

Sheathing - base of the leaf is wrapped around the stem like a grass leaf, as in Zea mays (corn) and Zingiber spp. (ginger).

Decurrent - leaf base extends downward to form a wing or ridge along the stem, as in Psidium guajava (guava).

Winged petiole - petiole has a leaf-like or membrane-like extension along its length, as in Citrus x paradisi (grapefruit).

Winged rachis - compound leaf stem with a membrane-like extension on both sides of the rachis, as in Rhus copallinum (winged sumac).

Stipule Types

Simple - stipules located on the sides of the petiole, as in Hibiscus rosa-sinensis (hibiscus).

Adnate - stipules which adhere to the sides of the petiole, as in Trifolium spp. (clover) and Rosa spp. (rose).

Leafy - green, leaf-like stipules which serve as foliage, as in Pisum sativum (pea) and Delonix regia (royal poinciana).

Other Leaf Types

Needle-shaped leaves - such as those in Pinus spp. (pines).

Needle-like leaves - margin of the leaf is so strongly rolled backward that the leaf appears tubular, such as in Ceratiola ericoides (Florida rosemary).

Awl-shaped and scale-like leaves - very reduced leaves, as in Platycladus orientalis (arbor vitae), Taxodium ascendens (pond cypress), and adult Juniperus silicicola (red cedar).

Leaf Textures

Succulent - juicy, fleshy, soft, and thickened in texture.

Scabrous - rough to the touch; texture of sandpaper.

Coriaceous - leather-like, tough.

Smooth (glabrous) - surface is not hairy, rough, pubescent, or scabrous.

Downy - covered with very short, weak, and soft hairs.

Pubescent - hairy.

Canescent - covered with gray or white soft hairs as in Leucophyllum frutescens (Texas sage).

Tomentose - covered with matted, woolly hairs.

Hirsute - pubescent with coarse, stiff hairs.

Hispid - rough with bristles, stiff hairs, or minute spines.

Source: Botany Handbook for Florida, Revised Edition, Kathleen C. Ruppert, January 1999 -- This document is copyrighted by the University of Florida, Institute of Food and Agricultural Sciences (UF/IFAS) for the people of the State of Florida. UF/IFAS retains all rights under all conventions, but permits free reproduction by all agents and offices of the Cooperative Extension Service and the people of the State of Florida. Permission is granted to others to use these materials in part or in full for educational purposes, provided that full credit is given to the UF/IFAS, citing the publication, its source, and date of publication.

 

 
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