Plant Taxonomy Prof.(Dr.)Punam Jeswal Head B.Sc (Hons.) Part ll Botany Department
Cronquist's System of Classification of Angiospermic Plant
Cronquist's System Arthur Cronquist, a curator of New York Botanical Garden proposed a system of classification in his book entitled -"The Evolution and Classification of Flowering Plants" (1968), it is elaboration and modification of a scheme presented in 1957 under the title "Outline of a New System of Families and Order's of Dicotyledons". The latest version of his system appeared in 1981 in "An Integrated System of Classification of Flowering Plants" where he divided the division Magnoliophyta (Angiosperms) into two classes; Magnoliopsida and Liliopsida.
Salient Features
Cronquist considered Pteridosperms (seed ferns) as probable ancestors of angiosperms. His ideas of evolutionary trends among angiosperms are that :
1. The primitive angiosperms are evergreen trees or perhaps large shrubs and herbs are advanced.
2. Simple and entire leaves are primitive.
3. Pinnately net veined leaves are primitive as compared to parallel veined leaves.
4. The primitive stomata are ranunculaceous type from which other types have been derived.
5. The nodes are probably unilacunar with two traces or perhaps trilacunar in primitive angiosperms.
6. Vessel less wood is primitive than with vessels.
Angiosperms
2 Classes
Magnoliopsida Liliopsida (Dicots) (Monocots)
6 Subclasses
Magnolidae Hamamelidae Caryophyllidae Dillenidae Rosidae Asteridae
(8 Orders) (11 Orders) (3 Orders) (13 Orders) (18 Orders) (11 Orders)
5 Subclasses
Alismatidae Arecidae Commelinidae Zingiberidae Liliidae
(4 Orders) (4 Orders) (7 Orders) (2 Orders) (2 Orders)
Fig. Outline Classification of Arthur Cronquist
7. The primitive flowers are large and terminal which has numerous spirally arranged large and free tepals.
8. Stamens are numerous and leaf like, spirally arranged in primitive flowers.
9. Unisexual flowers are derived from bisexual flowers.
10. Primitive pollen is uniaperturate with a long sulcus from which triaperturate is derived.
11. Pollination by beetles that chewed and ate the parts of the flower is primitive and wind pollination derived from it.
12. Carpels is primitive flower are numerous, spirally arranged, leaf, like and probably stipitate. Each carpel has numerous ovules and margins provided with tuft of hairs. Reduction in number of carpels and their fusion is found in advanced taxa.
13. Anatropous, bitegmic ovules with massive nucellus is primitive and other types are derived from it.
14. Among embryo sacs, Polygonum 8- nucleate embryo sac is most primitive and others are derived from it.
15. Nuclear endosperm is primitive and cellular and helobial are advanced.
16. Dicotyledonous embryos with two cotyledons are primitive and the monocot embryo is advanced.
Critical Comments
Merits
1. Magnoliales comprising 17 families are treated as most primitive order among the angiosperms and kept in the beginning.
2. Family Canellaceae which was placed under Parietales has been shifted to Magnoliales.
3. Family Ceratophyllaceae which was placed under ordines anomali, is shifted to aquatic Nymphaeales.
4. Aristolochiaceae of Multiovulatae Terrestres has been placed near Magnoliales.
5. Papaveraceae and Fumariceae are treated separate families and kept under the order Papaverales.
6. Urticales comprising Urticaceae, Ulmaceae, Moraceae etc. are placed under subclass Hamamelidae.
7. Cactaceae is included under Caryophyllales (= Centrospermae).
8. Paeonia is treated as a separate family from Ranunculaceae, and placed under Dilleniales.
9. Podostemaceae is placed after Rosales.
10. Cuscutaceae is separated from Convolvulaceae.
11. Callitrichaceae is placed under Lamiales along with Labiatae and Verbenaceae.
12. Compositae (Asteraceae) is placed at the top of Dicotyledons.
13. Alismatales including Butomaceae, Alismataceae are placed in the beginning of the monocots.
14. Orchidaceae are placed at the top of monocotyledones.
15. Anatomical, playnological, embyrological evidences have been taken into consideration.
16. Dicotyledones have been placed before monocotyledones.
Demerits
1. In Violales (=Parietales), inclusion of Tamaricaceae and Frankeniaceae is not justified because they differ from other families of the order in having NPC formula 345. In Parietales it is 434. Hutchinson kept these in a separate order Tamaricales.
2. The family Cornaceae that shows strong affinities with Araliaceae and Umbelliferae has been separated from that alliance and kept under Cornales of subclass Rosidae while the other two have been placed under Apiales.
3. The family Lecythidaceae that is closely allied to Myrtales has been placed under order Lecythidaceae of subclass Dillenideae while Myrtales have been placed under subclass Rosidae.
4. Cyperaceae and Poaceae (Gramineae) have been placed together under Cyperales, but the studies have shown that these two families are quite distinct. Hutchinson and Takhatajan rightly placed them under separate orders.
5. Placing of Liliales after Arecales and Cyperales is not justified, because these two orders are supposed to have Liliaceaeous ancestry.