Evolutionary Botany: From Mendel to Modern Plant Speciation

Evolutionary botany traces how plant diversity arose through genetic change, natural selection, and speciation. Its modern synthesis blends genetics, cytology, paleobotany, and ecology.

Foundational Works

• 1866: Mendel's pea experiments—laws of inheritance (rediscovered 1900).
• 1937: Dobzhansky's Genetics and the Origin of Species—modern synthesis.
• 1950: Stebbins' Variation and Evolution in Plants—plant-specific mechanisms (polyploidy, hybridization).
• 1950: Darlington & Mather's Genes, Plants, and People—chromosome evolution.
• 1951: Clausen's Stages in Evolution of Plant Species—ecotypes.
• 1963/1971: Grant's Origin of Adaptations & Plant Speciation—reproductive isolation.

Key Plant Evolutionary Themes

• Polyploidy: Whole genome duplication—instant speciation, common in angiosperms (wheat, cotton, many crops).
• Hybridization: Interspecific crosses → new lineages (e.g., Helianthus sunflowers).
• Selfing vs. Outcrossing: Mating system evolution drives floral morphology.
• Coevolution: Pollinators, herbivores, dispersers shape traits.
• Molecular clocks: DNA sequences date divergences.

Morphological Terms with Evolutionary Significance

Bract

Modified leaf near flower/inflorescence. Protects buds. Often showy (poinsettia, dogwood, bougainvillea). Smaller than foliage leaves. Taraxacum (dandelion) bracts are tiny scales.

Brachyblast (Short Shoot)

Condensed stem with very short internodes. Bears flowers (angiosperms) or leaf clusters (pines, ginkgo). Concentrates reproductive structures.

Bulbs & Underground Storage

Survival structures in seasonal climates.

• Tunicate: Concentric scales (onion, tulip, narcissus, hyacinth). Papery tunic.
• Imbricate (Scaly): Overlapping scales, no tunic (lily).
• Parts: Basal plate (roots), scales (storage), tunic, central bud (flower), lateral buds (bulbils).
• Genera: Allium, Narcissus, Tulipa, Lilium, Hyacinthus, Camassia, Fritillaria, Galanthus, Hippeastrum, etc.

Orchid pseudobulbs are aerial analogs.

Evolutionary botany reveals plants as dynamic lineages, not static classifications—shaped by genome duplications, ecological negotiations, and the relentless filter of selection.