Leaf Terminology (Part 2)

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Botany 115 Terminology

Leaf Terminology Part 2

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Inflorescence Terminology Part 1
Inflorescence Terminology Part 2

5. Leaf Shapes

A. The Prefix "Ob" In A Descriptive Leaf Term

B. Images Of Leaf Shapes

6. Leaf Apices

7. Leaf Bases

8. Leaf Margins

9. Leaf Surfaces

Botanical terms that describe the surfaces of leaves and stems:

  • Glaucous: Covered with a whitish powder or waxy coating.
  • Farinose: Covered with a meal-like powder or minute particles.
  • Scurfy: Covered with small scalelike particles.
  • Viscid (Viscous): Covered with sticky or resinous secretion.
  • Glutinous: About the same as viscid.
  • Punctate: Dotted with minute pits or translucent dots.
  • Papillate (Papillose): Bearing minute, pimplelike protuberances.
  • Tuberculate: Bearing tubercles or warty protuberances.
  • Verrucose: About the same as tuberculate
  • Rugose: Wrinkled--typical leaves of the mint family (Lamiaceae)
  • Glabrous: Without hairs of any kind.
  • Pubescent: With a hairy surface--there are many kinds of hairiness:

Note: In the goosefoot family (Chenopodiaceae), many species have herbage covered by farinose
(mealy) trichomes. This is particularly evident in the genus Chenopodium, such as C. murale. The
surface of a leaf or other structure covered by these peculiar, sessile, water-filled vesicles appears
to be coated with minute beads.  When these trichomes dry out, the surface appears to be coated
with a dusting of flour-like particles.

See Vegetables of the Goosefoot Family (Chenopodiaceae)

The characteristic rugose (wrinkled) leaves of Rosa rugosa. The bright orange-red structures are rose hips, the achene-bearing, aggregate fruit of a rose.

21 Types of Hairiness or Fuzziness (Some Are Redundant):

  1. Arachnoid: Cobwebby--soft, entangled hairs.
  2. Barbellate: Hairs with barbs down the sides.
  3. Bearded: Long, stiff hairs.
  4. Bristly: Stiff hairs.
  5. Canescent: Dense grayish-white hairs.
  6. Ciliate: Hairs along leaf margin forming a fringe.
  7. Floccose: Tufts of soft, woolly hairs.
  8. Glandular: Hairs with enlarged gland at tip.
  9. Hirsute: Stiff hairs, rough to the touch.
  10. Hispid: Stiff (rigid), bristly hairs--may penetrate skin.
  11. Hoary: Covered with short fine hairs (white down).
  12. Lanate: Woolly or cottony hairs.
  13. Pilose: Sparse, soft and straight hairs.
  14. Puberlulent: Minutely pubescent (diminutive of pubescent).
  15. Scabrous: Rough to the touch due to short, stiff hairs.
  16. Sericeous: Appressed, fine and straight hairs (silky).
  17. Stellate: Star-shaped hairs (common in Malvaceae).
  18. Strigose: Sharp, straight, appressed hairs.
  19. Tomentose: Densely matted, soft white wool (tomentum).
  20. Villous: Long and soft hairs (shaggy)--not matted.
  21. Woolly: Long, soft entangled hairs (similar to tomentose).

The glistening, gland-tipped hairs (trichomes) on the stem of the desert wildflower appropriately named
tackstem (Calycoseris wrightii) resemble minute translucent tacks. Magnification approximately 15x.

Gland-tipped hairs on a rose bud. The dark aphid nymphs are 0.9 mm in length.

Rose bud photographed with Nikon D-90 and 60mm macro lens. The aphid nymph and gland-tipped hairs appear almost as large as in the above microscope image, but they are sharper.

Many specific epithets (2nd element of binomial) are derived from the above terms for leaf and stem surfaces.
Aquilegia pubescens
Arctostaphylos glandulosa
Arctostaphylos glauca
Lupinus hirsutissimus
Lotus strigosus
Ceanothus tomentosus
Ceanothus verrrucosus
Ceanothus papillosus
Chenopodium farinosum
Encelia farinosa
Baccharis glutinosa
Eriophyllum lanatum

The leaves and stems of ice plant (Mesembryanthemum crystallinum) are covered with vesicular papillae.

What is the adaptive significance of these different surfaces which are genetically determined?

  1. Insulation: These surfaces may prevent excessive water loss due to transpiration as dry winds blow across leaves and stems. In some species, the stomata are sunken in pits or in crypts lined with hairs. Leaves of chaparral shrubs, such as scrub oaks (Quercus) and California lilac (Ceanothus), have their stomata confined to the undersides, covered by a dense layer of hairs. The stomata are on the shady side of the leaf and out of the direct sunlight. The dense layer of hairs provides insulation and humidty around the guard cells so they remain turgid. If the guard cells become wilted or flaccid, the stoma closes, and gas exchange cannot occur. Insulation also shields plants from intense solar radiation and severe cold and frost. The latter extreme conditions of aridity and frost may occur during the summer months in alpine regions of the Sierra Nevada (above 12,000 feet). Intense sunlight with UV is especially severe in the alpine zone when combined with highly reflective rock and snow surfaces.

    See Leaves Of Scrub Oaks In San Diego County

    Plants carry on gas exchange through minute pores called stomata. Carbon dioxide from the atmosphere enters the stomata and oxygen produced by photosynthesis diffuses out of the stomata. Water molecules also escape through the stomata, especially in hot, dry weather. Water loss through the stomata is known as transpiration. If the plant loses too much water it will wilt and eventually die. To cope with this dilemma, plants have evolved paired guard cells on each side of the stoma. When the guard cells are fully turgid or expanded, they have an elongate opening (stoma) between them. The walls adjacent to the stoma are very thin and flexible, while the outer walls on the opposite sides of the stoma are much thicker and more rigid. This differential thickening causes an opening to develop when the guard cells are inflated by internal water pressure (called turgor pressure). When the guard cells lose water on a hot day, they become deflated and push together, thus closing off the stoma. This cleaver strategy prevents the plants from losing excessive water through transpiration. See the following highly magnified view of the paired guard cells:

    The leaf surface of a species of Tradescantia, also known as spiderwort (Commelinaceae), a plant that is commonly grown in hanging baskets. Note the paired guard cells and stoma (opening slit) between them (circled in red). Also note the scattered hairs (trichomes). Each hair arises from a pedestal-like basal cell containing a nucleus.

    Microscopic view of the paired guard cells and stoma on the leaf surface of spiderwort (Tradescantia). An opening or stoma develops between the inflated (turgid) guard cells due to a differential thickening of their walls. When the guard cells lose water pressure on a hot day, they deflate and push together, thus closing off the stoma and reducing water loss (transpiration) through the leaf.

  2. Light Reflection: Many desert and alpine plants have light-colored or silvery pubescence which reflects intense sunlight. This remarkable topic is discussed by Zwinger and Willard in Land Above the Trees (1972). In addition to various types of pubescence, there are other surfaces which provide effective insulation and reflection. These latter adaptations include resinous (glutinous) coatings, powdery or waxy coatings (glaucous), and other surfaces, such as scurfy and farinose. There are many other morphological, anatomical and physiological adaptations to environmental extremes of drought and temperature.

    See The Remarkable Silver Sword Of Haleakala Crater

  3. Deciduous: The leaves of many angiosperm trees fall from the branches during the autumn months, thus preparing the trees for their winter dormancy period. A special layer of cells at the base of the petiole, called the abscission layer, is controlled by growth hormones, such as auxin and ethylene. The abscission layer neatly separates the leaf from its stem, thus causing it to fall with the slightest breeze. In cold climates of northern latitudes it is vital to have all the branches devoid of leaves, so that snow falls through the branches. Without an abscission layer, persistent dead leaves attached at their petioles could collect snow, thus causing the limbs to break under the heavy weight.

    Flavonols are colorless or yellow flavonoids found in leaves and many flowers. Quercetin is the yellow flavonol pigment of oak pollen. The fall coloring of deciduous trees may involve yellow carotenoid pigments (terpenes) as well as flavonoids. In some trees, such as red maple (Acer rubrum) and scarlet oak (Quercus coccinea), colorless flavonols are converted into red anthocyanin as the chlorophyll breaks down. Contrary to some references, bright red autumn leaves can develop without a frost. The following leaves of two eastern U.S. trees, including sweet gum (Liquidambar styraciflua) and pin oak (Quercus palustris), turned red in coastal San Diego County without any frost. The trees are genetically programmed to drop their leaves in the fall, and red anthocyanins replace chlorophylls in the leaves.

Sweet gum (Liquidambar styraciflua) and Texas red oak (Quercus buckleyi).

Sugar maple (Acer saccharum) in the Eastern United States.

10. Conifer Leaves

11. Typical Leaf Of The Grass Family (Poaceae)

In herbaceous (nonwoody) grasses, such as wheat, rice, barley and oats, each leaf has a basal sheath that envelops the grass stem (culm) down to its point of origin (node). At the upper end of each culm sheath is the actual leaf blade, which typically extends away from the culm. At the junction of the sheath and blade is a small, membranous scale called the ligule. Minute projections at the base of the leaf blade are called auricles. Grass leaves grow from an intercalary meristem at the base of the sheath in the node region. This is why the tranversely cut blades of grass plants in your lawn grow upwardly, even though you mowed them off the previous week. The meristematic region of herbaceous annual and perennial grasses is at the base of the leaves and continually produces more leaf tissue. This is undoubtedly an adaptation to grazing animals which could destroy the grass plant if the vulnerable growth regions were apical rather than basal. Flowering (seed-bearing) stems of cereal grasses develop from apical meristems that generally do not resprout if the peduncle (flower stalk) is severed. Annual grasses (including many weedy grasses in San Diego County) die following their blooming cycle. Perennial grases die back to the rhizome and resprout the following year. The structure and growth of bamboo leaves is very different from herbaceous grasses. It is explained at the Wayne's Word article about bamboo.

Annual blugrass (Poa annua), a common naturalized weed in southern California. The leaf blade extends down the culm as an enveloping sheath to a slightly enlarged point of attachment on the culm called the node. At the junction of the leaf blade and culm sheath is a small scalelike ligule. The floret consists of two bracts called the palea and lemma. Within the floret is the apetalous, bisexual grass flower consisting of a gynoecium (pistil) and three stamens (androecium). Following pollination and fertilization, the ovary develops into a one-seeded fruit called a grain or caryopsis. In some grasses, the minute remnants of perianth segments called lodicules are visible at the base of the ovary. Grasses are typically wind-pollinated, although some species have cleistogamous, self-pollinated flowers that remain closed within the bracts of the floret.

Bamboo: A Remarkable Giant Grass

See Vegetative Terminology (Parts I, II, III)
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