Plant Science 1 (Hort. 1007) Course Notes

Introduction to Horticulture and Plant Classification

• Etymology of Horticulture:

  • Derived from the Latin words Hortus (garden) and cultura (cultivation).

  • Unlike agriculture, which focuses on large-scale crop production (agronomy), horticulture traditionally focuses on individual plant care and garden management.

• Branches of Horticulture:

  • Olericulture: The science of growing vegetables.

  • Pomology: The study and cultivation of fruits and nuts.

  • Floriculture: The production and marketing of floral crops.

  • Landscape Horticulture: The design, installation, and maintenance of outdoor spaces.

• Classification Challenges:

  • There are approximately $400,000$ known plant species. Systems of categorization are essential to communicate across different languages and regions without ambiguity.

Historical Evolution of Plant Taxonomy

• Early Systems:

  • Aristotle (4th century BCE): Classified plants by size and habit (trees, shrubs, and herbs).

• The Renaissance Transition:

  • Andrea Cesalpino (1583): One of the first to classify plants based on reproductive organs (fruits and seeds) rather than just growth habit.

  • John Ray (Late 17th Century): Introduced the concept of the species and differentiated plants into monocotyledons and dicotyledons.

• The Linnaean Revolution:

  • Carl Linnaeus ($1707$-$1778$): Known as the "Father of Taxonomy." He published Species Plantarum ($1753$), which established the sexual system of classification and the universal use of Binomial Nomenclature.

The Taxonomic Hierarchy

Plants are organized into a nested hierarchy to show evolutionary relationships:

1. Kingdom: Plantae (Multicellular, eukaryotic, photosynthetic organisms).

2. Division (Phylum):

   • Bryophytes: Non-vascular plants (e.g., mosses).

   • Pteridophytes: Seedless vascular plants (e.g., ferns).

   • Gymnosperms: "Naked-seed" plants (e.g., conifers).

   • Angiosperms: Flowering plants (e.g., lilies, oaks).

     • Class Magnoliopsida (Dicots): Two seed leaves, netted veins.

     • Class Liliopsida (Monocots): One seed leaf, parallel veins.

3. Order: Groups of families with similar floral structures.

4. Family: Plants with shared evolutionary traits; names usually end in -aceae (e.g., Rosaceae).

5. Genus: A group of plants with very similar morphological characteristics.

6. Species: The basic unit of classification; a group of individuals capable of interbreeding to produce fertile offspring.

Binomial Nomenclature Protocols

• The Scientific Name: Consists of two parts in Latin (a "dead" language chosen for its stability and universal use).

  • Genus: Always capitalized and italicized (or underlined).

  • Specific Epithet: Always lowercase and italicized (or underlined).

  • Example: Quercus alba (White Oak).

• Authority Citation: A letter or abbreviation following the name indicates the person who first described the species.

  • Example: Solanum tuberosum L. (The "L." stands for Linnaeus).

Classification by Life Cycle and Growth Habit

• Life Cycles:

  • Annuals: Complete their entire life cycle (germination to seed production) in one growing season.

  • Biennials: Require two growing seasons; vegetative growth in the first, flowering and death in the second (e.g., carrots, foxglove).

  • Perennials: Live for more than two years. They may be herbaceous (die back to the ground) or woody.

• Tissue Types:

  • Herbaceous: Soft, green stems; usually die back in winter.

  • Woody: Possess secondary xylem (wood) and bark; survive winter above ground.

• Leaf Retention:

  • Deciduous: Lose all leaves during a specific season (dormancy).

  • Evergreen: Retain leaves year-round; individual leaves are shed at different times.

Distinctive Categories: Variety vs. Cultivar

• Variety (var.): A naturally occurring sub-group within a species that displays unique traits inherited consistently through seed.

  • Example: Gleditsia triacanthos var. inermis (Thornless Honey Locust).

• Cultivar (cv.): Short for "cultivated variety." These are bred or selected by humans for specific traits. They are usually propagated asexually (cloning) to maintain genetic integrity.

  • Formatting: The name is written in single quotes and not italicized.

  • Example: Acer rubrum 'Red Sunset'.

Modern Trends in Taxonomy

• Phylogenetics: Modern classification relies heavily on DNA sequencing rather than just morphology (physical appearance). This has led to the reclassification of many families as we discover true genetic lineages.

Professional Opportunities in Horticulture

• Production: Greenhouse management, nursery operations, viticulture (grapes).

• Management: Turfgrass management (golf courses, sports fields), arboriculture (tree care).

• Design & Service: Landscape architecture, interior plantscaping, floral design.

• Media & Education: Horticultural therapy, research science, botanical garden curation, and agricultural journalism.