Plant Morphology - Comprehensive Study Notes

Growth (Life) Form

• Definitions
  • Herbaceous: primary growth only; stems typically last about $ext{one year} \, ( ext{approximately } 1 ext{ year})$; wood is absent.
  • Woody: wood and bark produced by secondary growth; stems grow in diameter over time; stems may last many years.
• Examples (OK specimens listed in the transcript)
  • Herb (forb): Green Antelopehorn, $Asclepias viridis$ (Apocynaceae).
  • Shrub (woody): American Beautyberry, $Callicarpa americana$ (Lamiaceae).
  • Vine: Baldwin’s Milkvine, $Matelea baldwyniana$ (Apocynaceae).
  • Tree (woody): Mexican Plum, $Prunus mexicana$ (Rosaceae).
• Epithets of life forms (epiphyte is listed as a growth form)
  • Epiphyte examples: Orchid, $Epidendrum ext{ sp.}$ (Orchidaceae); Bromeliad, $Vriesia ext{ sp.}$ (Bromeliaceae); Cactus, $Epiphyllum ext{ sp.}$ (Cactaceae).

Shoots and Roots

• Definition by seedling development
  • Shoot: upper part of the seedling.
  • Root: lower part of the seedling.

Plant Architecture: Modules

• Key terms (Fig. 36.3 references the concept of modular growth)
  • Node: place on stem where leaves are attached.
  • Internode: space on the stem between nodes.
  • Apical bud: meristem at the tip of the stem where new stem and leaves are produced.
  • Axillary bud: meristem between leaf and stem (in the axil).
  • Meristem: tissue where new cells are produced.
  • Primary Growth: production of new modules (growth in length, not diameter).
• Example: Matelea adenocardia (Apocynaceae)
  • Shoot modules: repeated production of similar (homologous) structures.

Leaf Shoot Structure

• Key components
  • Node
  • Internode
  • Axillary bud
• Example: Cashew, $Anacardium occidentale$ (Anacardiaceae) shows node-associated leaf/axillary features.

Nodes

• Nodes as sites of axillary activity
  • Nodes can give rise to flowers from axillary buds (depending on species).
  • Example: Feverwort, $Triosteum perfoliatum$ (Caprifoliaceae) demonstrates a leaf at a node with potential floral development from the axillary region.
  • Concept: the “node” is the critical junction for leaf attachment and axillary meristem activity.

Leaf Structure: Petiole & Blade

• Components
  • Petiole: stalk attaching blade to the stem.
  • Blade (lamina): the leaf blade itself.
• Example: Clover Ash, $Tetrazygia sp.$ (Melastomataceae) illustrates blade-petiole organization.

Leaf Structure: Stipules

• Stipules: small leaf-like appendages at the base of the petiole.
• Composite view: blade (lamina), petiole, stipules present at the node; venation and bud location can be associated with stipules.
• Example image reference: Acalypha sp. (Euphorbiaceae) showing stipules.

Leaf Arrangement: Sessile Leaves

• Example: Ashy Sunflower, $Helianthus mollis$ (Asteraceae) with sessile leaves (petiole absent or very short).

Leaf Composition: Simple

• Simple leaf: a single blade per leaf.
• Example: Clover Ash, $Tetrazygia sp.$ (Melastomataceae) demonstrates simple leaf structure.

Leaf Composition: Pinnately Compound

• Structure: a major axis (rachis) with multiple leaflets along its length.
• Example: Green Ash, $Fraxinus pennsylvanica$ (Oleaceae);
  • Key features shown: leaflet arrangement along a rachis; presence of a bud at the base; axillary bud is key to identifying a compound leaf.
• Important terms: leaflet, rachis, petiole, leaflets, and the central rachis.

Leaf Composition: Palmately Compound

• Examples:
  • Small Fuzzybean, $Strophostyles leiosperma$ (Fabaceae) – palmately arranged leaflets.
  • Also noted: Trifoliate forms exist within palmately compound configurations.
• Concept: multiple leaflets radiate from a common point (petiole or rachis base).

Leaf Arrangement (OK examples)

• Alternating arrangement: Feverwort, $Triosteum perfoliatum$ (Caprifoliaceae) exemplifies alternate leaves.
• Opposite arrangement: Salal, $Gaultheria shallon$ (Ericaceae) exemplifies opposite leaves.
• Whorled arrangement: Horsetail Milkweed, $Asclepias verticillata$ (Apocynaceae) demonstrates whorled leaves.
• Note: The transcript lists several arrangements with family-level associations.

Leaf Blade Shape: Key Concepts

• Core question: How wide is the leaf relative to its length? Where is the widest point (middle, towards tip, or towards base).
• Source reference: Michelle Nakano, LibreTexts.

Leaf Blade Shapes

• Linear: slender and longer than wide.
• Orbicular: circular/rounded shape.
• Ovate: egg-shaped, wider near the base.
• Lanceolate: spear-shaped, widest above the base.
• Obovate: inverse-ovate, wider toward the tip.
• Oblong: longer than wide with nearly parallel sides.
• Examples cited: Auricled Milkweed, $Asclepias engelmanniana$ (Apocynaceae); Ant Plant, $Dischidia oiantha$ (Apocynaceae).

Leaf Base Shape

• Cordate: heart-shaped base.
• Cuneate: wedge-shaped base tapering to the stem.
• Examples: Frangipani, $Plumeria rubra$ (Apocynaceae); Baldwin's Milkvine, $Matelea baldwyniana$ (Apocynaceae).

Leaf Apex Shape

• Acute: sharp tip.
• Obtuse: blunt tip.
• Examples: Two-flowered Milkvine, $Matelea biflora$ (Apocynaceae); Adder's Tongue, $Ophioglossum engelmannii$ (Ophioglossaceae).

Leaf Blade Margin

• Entire: smooth, non-toothed edge.
• Lobed: jawed or lobed edges.
• Crenate: small rounded teeth.
• Serrate: sharp, saw-toothed edges.
• Examples: Redbud, $Cercis canadensis$ (Fabaceae) – entire; Post Oak, $Quercus stellata$ (Fagaceae) – lobed.

Leaf Venation

• Palmate: multiple main veins radiating from a single point (like a hand).
• Pinnate: a single main vein with smaller veins off to the sides.
• Parallel: veins run parallel to each other.
• Examples: Redbud, $Cercis canadensis$ (Fabaceae) – palmate; Cascara Buckthorn, $Frangula purshiana$ (Rhamnaceae) – pinnate; Yellow Lady’s Slipper, $Cypripedium parviflorum$ (Orchidaceae) – parallel.

Indumentum (Vestiture) of Trichomes

• The term refers to surface hairs or trichomes on plant parts.
• Example image: Solanum atropurpureum (Solanaceae) showing prickles and both glandular and eglandular trichomes.
• Definitions/grades used in the notes:
  • Glabrous: lacking hairs.
  • Hirsute: hairy.
  • Tomentose: densely woolly/hairy.
  • Pubescent/Puberulent: covered with soft short hairs of varying density.
• Examples:
  • Glabrous: Corn-kernel Milkweed, $Asclepias latifolia$ (Apocynaceae).
  • Hirsute: Butterflyweed, $Asclepias tuberosa$ (Apocynaceae).
  • Tomentose: $Asclepias ext{ new species}$ (Apocynaceae).
  • Puberulent: $Asclepias oenotheroides$ (Apocynaceae).

Leaf Modifications

• Bracts, spines, traps as modifications to aid in pollination, defense, or prey capture.
• Examples:
  • Pitcher Plant, $Nepenthes sp.$ (Nepenthaceae) – trap-type modification.
  • Flowering Dogwood, $Cornus florida$ (Cornaceae) – bracts associated with inflorescence.
  • Tuna Colorada, $Opuntia stenopetala$ (Cactaceae) – spiny/trap-like structures.

Stem Modifications

• Water storage (above ground): organs enabling water storage.
  • Example: Organ Pipe, $Stenocereus thurberi$ (Cactaceae).
• Rhizomes, Stolons, and Tubers
  • Rhizome: underground horizontal stem that produces new individuals at nodes below ground.
  • Stolons: above-ground horizontal stems producing new individuals at nodes.
  • Tubers: storage organs for carbohydrates.
  • Visual reference: Fig. 36.10 from S. Freeman (2008).
• Other stem modifications: Thorns added for defense (example: Honey Locust, $Gleditsia triacanthos$).

Stem Absence and Presence

• Caulescent: stems present.
• Acaulescent: stems absent or very short.
• Example notes: Acaulescent plant examples include Aechmea sp. (Bromeliaceae) and some Asclepias species with very short or inconspicuous stems.

Roots

• Taproot: a single thick vertical root with smaller lateral roots.
  • Example: Carelessweed, $Amaranthus palmeri$ (Amaranthaceae).
• Fibrous roots: many thin roots of similar size.
  • Example: Yellow Foxtail, $Setaria pumila$ (Poaceae).
• Root Modifications
  • Adventitious roots (roots that arise from non-root tissue) that may perform various functions (e.g., storage, photosynthesis).
  • Red Mangrove, $Rhizophora mangle$ (Rhizophoraceae) as a classic example of adventitious roots in mangroves.
  • Radish, $Raphanus sativus$ (Brassicaceae) as an edible example with notable root structure.
• Root Modifications - Knees
  • Function: Knees (pneumatophores) are thought to aid gas exchange in water-logged soils (noting their occurrence in Bald Cypress, $Taxodium distichum$, Cupressaceae).

For Next Time / Study Tips

• Review terms for vegetative morphology
• Carefully study illustrated terms in the Plant Identification Terminology textbook
• Practice walking around campus to apply these terms in real plants; peers will be impressed with your accuracy and vocabulary