Plant Taxonomy Prof.(Dr.) Punam Jeswal Head B.Sc (Hons.) Part ll Botany Department

Bentham and Hooker's System of Classification of Angiospermic Plant

Bentham and Hooker's System -

Two British Botanists associated with Royal Botanic Gardens. George Bentham and Joseph Dalton Hooker jointly published a system of classification in three volumes of Genera Plantarum, published in Latin from 1862 to 1883.

Silent features -

1. This system was fundamentally based on that of Augustin Pyramus de Candolle (1778-1841), but disagreed in many respects.

2. They emphasized much on the nature of perianth, especially number of whorls (one or two) and if two, whether the members of inner whorl(petals) are free or fused.

3. In Genera Plantarum, 97, 205 species under 7,569 genera of seed plants known to them, have been described and classified.

4. The spermatophytes are divided into three classes viz. Dicotyledons, Gymnospermae and Monocotyledons, which are further divided into 3 subclasses, 21 series, 25 cohorts(orders) and 202 natural orders (families).

5. Out of 202 families recognized by them, three belong to Gymnospermae and 199 to angiosperms.

6. The dicots are divided into three subclasses viz. Polypetalae, Gamopetalae and Monochlamydeae, depending on the free or fused nature of petal or perianth in one whorl.

7. The Family -Ranunculaceae (Ranales) are considered to be most primitive, therefore placed in the beginning and Family- Gramineae (Poaceae) are considered to be most advanced, therefore placed in the end.

Spermatophyta or Phanerogams 3 Classes

Dicotyledons Gymnospermae Monocotyledons

3 Subclasses

Polypetalae Gamopetalae Monochlamydeae

3 Series 3 Series

Series

Series Thalamiflorae Disciflorae Calyciflorae Inferae Heteromerae Bicrpellatae

1 Curvembryeae 2 Multiovulatae aquaticae 3.Multiovulatae terrestris 4.Micrembryeae 5 Daphnales 6 Achlamydosporeae 7 Unisexuales 8 Ordines anomali

1. Microsperme 2. Epigynae 3. Coronarieae 4. Calycinae 5. Nudiflorae 6. Apocarpae 7. Glumaceae

Fig. Outline Classification of Bentham and hooker

Critical comments -

Since Charles Darwin was a close friend of Hooker therefore, he was inclined to reorganized the whole system according to the theory of evolution. However, Bentham did not accept the essential of Darwin's work and conceived pre-evolutionary thought that species are special creations, therefore constant and immutable. Thus, the system could not attain phylogenetic status, yet both the ideas are very well reflected in this system and concluded as to be natural one with following merits and demerits.

Merits -

1. The system is very useful from practical point of view because of greater number of categories; each category is well defined with distinguishing characters.

2. Although the system is not phylogenetic, yet placing of Ranales in the beginning of the dicots, justify the order being most primitive among the flowering plants. Similarly, the placing of Umbellales in the end of Polypetalae also reflects phylogenetic pattern because this order is regarded as most advanced among polypetalous group.

3. placing of monocots after the dicots is justified by majority of taxonomists today and favour the origin of monocots from dicots.

4. The natural orders(families) of disputed nature were placed under Ordines anomali.

5. The larger taxa were divided into smaller subcategories to bring more clarity.

6. The system is very handy for the purpose of quick identification of plants in the field.

Demerits -

1. Placing of Gymnospermae between Dicotyledons and Monocotyledons is extremely objectionable because Gymnosperms constitute a different class than angiosperms.

2. Several important floral characters have not been given proper respect, which they deserve.

3. In this system several closely related families (natural orders) have been separated and placed under different orders (cohorts). Concurrently numbers of unrelated families have been closely placed.

4. Subclass - Monochlamydeae is very heterogeneous and superfluous group because the families placed under different series of this class exhibit closer affinities with different families of Polypetalae, therefore various families therein can very well be distributed among various taxa of subclass- Polypetalae. Some important instances are -

(a) Families like Amarantaceae and chenopodiaceae (subclass- Monochlamydeae; series- Curembryae) show affinities with family-Caryophyllaceae (order-Caryophyllinae, series- Thalamiflorae, subclass- Polypetalae).

(b) Family- Podostemaceae ( subclass- Monochlamydeae; series- Multiovulatae Aquaticae) are closely related to family- Saxifragaceae or Crassulaceae(order- Rosales, series-Calyciflorae, subclass-Polypetalae).

(c) Family- Laurinaeae (subclass-Monochlamydeae; series- Daphnales) are closely related to family- Magnoliaceae(order-Ranales, series- Thalamiflorae, subclass- Polypetalae).

(d) Family- Platanaceae (subclass-Monochlamydeae; series- Unisexuales) are regarded as allied to Rosales (family-Rosaceae, subfamily- Spiraeoideae.

5. In monocots, the authors did not follow the same principles as for dicots, instead they have placed the advanced series Microspermae (family- Orchidaceae) in the beginning, which is objectionable. It should be kept in the last not in the beginning.