George Bentham a great taxonomist and plant explorer Sir Joseph Dalton hooker a great plant geographer and English systematizes jointly presented a system of classification. Their classification was published in 3 volumes of genera plantarum. They are associated with royal botanical garden at kew and adopted a very comprehensive system of classification which is purely natural and most convenient and extremely suitable system for practical utility in identification of plants providing them, their respective taxon. Following discussion can prove this fact.
Main features of classification :
i) This system includes the names and descriptions of all genera, of seed plants known so far and classified accordingly.
ii) This system divided seed plants into 97,205 species under 202 order or families.
iii) They divide seed plants into three classes in sequence. Discotyledon, gymnosperm and monocotyledon.
iv) Dicots divided into 3-divisions and 14 series on the basis of the natural and visual characteristic which provides key for identification.
v) Diocts started with family Ranun Culaceae having free sepals and petals and indefinite number of stamens and carpels are free where as it ends with labiatale having fused sepals and petals with definite number of carpels and stamens.
vi) Among monocots out of seven series with epigenous flower i.e. orchidaceous and scitaminal were kept first and second respectively followed by with petaloid hypogenous flowers and finally ended with Graminae and Cyperaceous.
Class – I
Series-I – Thalami florae :
Petals and stamens hypogenous, Disc present.
It includes six orders viz: Ranales paraietaes, poly galinae, caryophyllales, Guttiferales and malvales.
Series – II Disc florae :
Flowers in which sepals distinct or may united calyx free from ovary, disc present, below the ovary stamens definite, petals uniseriate. This includes four orders like geraniales, sapindales etc.
Series – III Calyciflorae :
Sepals united to form calyxtuebe which surrounds the ovary or agnate to ovary, petals inserted in the calyx tube, ovary inferior.
It includes five orders like rosales myrtales, umbellales etc.
Division – II Gamopetalae :
Petals united, Flowers with distinct calyx and corolla. Stamens few, attached to corolla lobes.
Class – II (Group) Gymnospermae:
Flowers in cones, perianth absent, seed not enclosed by fruit or Pericarp. It includes 3 orders.
Class – III (Group) Monocotyledon :
Usually herbs, some are shrubs, seed with one cotyledon inembroyo.
It includes seven series, viz moscrospermae, Epigynae, Nudiflora, glumaceae etc.
From this classification it is understood that if we proceed from the beginning considering the morphological characters of a species we can easily identify it to place it in its specific taxon. Therefore this classification is widely used in all over the world herbaria for following reasons.
i) Every genera and species was studies from the actual specimens available in the British and continental herbaria and their descriptions were based on their detailed morphological studies and dissections of flowers.
ii) Description made in classification for each taxon based on actual examination of species.
iii) In the division polyetalae the new series disc florae is interpolated between, thalmin flora and caliciflorae of Decandle’s system and it is a refinement over Decandole’s classification.
iv) Cymnosperms placed as a third taxon and placed in between dicot and monocot.
v) Ranales is placed first in the dicot which is very reasonable.
vi) Monocot follow dicots, but the gymnosperms in between is anomally but it is justified.
vii) Monochlamydae is considered as highly evolved and polyetalae is the most primitive.
Thus Bentham and Hooker’s system of classification is a natural system and there is no doubt that it provides a key for identification of plants.