Botany · Ch 5 — Taxonomy and Systematic Botany
Natural system of classification
Natural system of classification
Botanists who came after Linnaeus realised that no single character (like stamen count) deserves more weight than any other - this insight sparked the approach to a NATURAL system of classification in France, whose first scheme (based on overall similarity across many characters) was presented by Antoine Laurent de Jussieu in 1789.
The most widely followed and best-regarded natural system was proposed by two English botanists, George Bentham (1800-1884) and Joseph Dalton Hooker (1817-1911), published across three volumes as Genera Plantarum (1862-1883), describing 202 families, 7,569 genera and 97,205 species. Seed plants were split into three major classes. Class I Dicotyledonae (two cotyledons, reticulate leaf venation, tap root system, tetramerous/pentamerous flowers) is further split by corolla type into three sub-classes: Polypetalae (free petals, dichlamydeous flowers), itself split by the thalamus's shape into Series Thalamiflorae (dome/conical thalamus, superior ovary; 6 orders, 34 families), Disciflorae (prominent disc-shaped thalamus, superior ovary; 4 orders, 23 families) and Calyciflorae (cup-shaped thalamus, inferior/half-inferior ovary; 5 orders, 27 families); Gamopetalae (united petals, dichlamydeous), split by ovary position/carpel number into Series Inferae (epigynous, inferior ovary; 3 orders, 9 families), Heteromerae (hypogynous, superior ovary, more than two carpels; 3 orders, 12 families) and Bicarpellatae (hypogynous, superior ovary, two carpels; 4 orders, 24 families); and Monochlamydeae (incomplete flowers, either apetalous or with an undifferentiated perianth called a 'perianth', sometimes both whorls absent entirely; 8 series, 36 families). Class II Gymnospermae (naked seeds) has just three families - Gnetaceae, Coniferae, Cycadaceae. Class III Monocotyledonae (one cotyledon, parallel leaf venation, fibrous root system, trimerous flowers) has 7 series and 34 families. …
What this figure shows. A branching classification-tree diagram: 'Seed plants' at the top splits into Class I Dicotyledonae, Class II Gymnospermae (3 families: Gnetaceae, Coniferae, Cycadaceae) and Class III Monocotyledonae (7 series, 34 families). Dicotyledonae further splits into Sub-class I Polypetalae, Sub-class II Gamopetalae and Sub-class III Monochlamydeae (8 series, 36 families). Polypetalae splits into Series (i) Thalamiflorae (6 orders, 34 families), Series (ii) Disciflorae (4 orders, 23 families) and Series (iii) Calyciflorae (5 orders, 27 families). Gamopetalae splits into Series (i) Inferae (3 orders, 9 families), Series (ii) Heteromerae (3 orders, 1 …