• The angiosperms appeared suddenly in Cretaceous age about 65 million years back.

• Charles Darwin described this sudden appearance of angiosperms as an ‘abominable mystery’. (symbolize)
• When angiosperms appeared for the first time in lower or upper Cretaceous, they were full-fledged like the trees and the herbs of today.

• The fossil records of the angiosperms also support their appearance full-fledged in lower or upper Cretaceous.
• The forms of cycads and conifers, which long dominated in the universe ØHowever, some workers do not agree with the doctrine of ‘abominable mystery’.
• According to H.H. Thomas (1936), the angiosperms of the past replaced many of older gymnosperms in esturine and marshy waters. (coastal waterbody and wetland waterbody)
• Graud Eury (1906) believes that the angiosperms came into existence through mutation.
• Guppy (1919) however, supported the view of mutation.
• Prof. Bertrand is of opinion that all the great groups of vascular plants (Pteridophyta, Gymnospermae and Angiosperms) not only arose quite independently of each other but also they originated simultaneously  (at the same time) as far back in the Archian period (2000 million years old—oldest).

• According to paleobotanical evidence there are three possibilities
• These are
• 1.That the angiosperms are monophyletic (common ancestor)  in their origin
• 2.That the angiosperms are monophyletic but they diverged quickly (go in different direction) in terms of geological time, into a different groups
• 3.That the angiosperms are polyphyletic (more than one ancestor group).
• Campbell (scientist) : does not believe in monophyletic origin of angiosperms.
• According to Thomas, the angiosperms were derived from various pteridosperms early in the Mesozoic period.
• Parkin also argues for the monophyletic origin of the angiosperms.
• In conclusion we can say, that the history of the angiosperms is still almost as great a mystery as it was in the time of Darwin. We do not know, when, where or from what the presumably most recent and now dominant large group of existing terrestrial plants arose.

• Lotsy and Anderson suggest that the angiosperms may have arisen as a result of hybridization between two gymnosperms.

• According to Hagerup, the origin of some angiosperms took place from Coniferales through Gnetales.

• According to Hutchinson, in certain groups, trees and shrubs are probably more primitive than herbs

Benettitales- Ranales theory (in respect to origin of Angiosperms)

A. Hallier’s view

•Hallier’s view (1906) regarding the origin of angiosperm is that Ranales, (e.g., Magnolia) seems to be related to Bennettitales and may have been derived from Cycadeoidea, and that the monocotyledons are an offshoot of the dicotyledons.

•But the differences in the anatomical structure of the wood, types of sporophylls, nature and position of ovules, etc., in two groups, i.e., Benettitales and Ranales, have led to difficulties in accepting this view.

•It is more probable that both the groups have evolved from a common ancestry and developed in unrelated parallel lines.

B. Arber and Parkin

They were of the opinion that the earliest monocotyledons were more primitive than the dicotyledons. They also supported the Hallier’s view.

C. Hutchinson

Hutchinson (1925) considered the origin of angiosperms as monophyletic, and supported the views of Hallier (1906) and Arber and Parkin (1907). He further held the view that the monocotyledons were derived from a primitive dicotyledonous order, the Ranales.

2. Coniferae-Amentiferae theory ( in respect to origin of Angiosperms)

• Engler and Prantl (1924) rejected view of Hallier (1906).
• They held the view that dicotyledons and monocotyledons had arisen independently from a extinct gymnosperms
• They considered the monocotyledons to be more primitive than the dicotyledons.
• But according to the modern classification these orders are regarded more advanced.

3. Gnetales-Casurinales theory (in respect to origin of Angiosperms)

Wettstein (1935) held the view that angiosperms of Casuarina type evolved from Gnetales, (particularly Ephedra), a highly advanced group of gymnosperm. Thus both Gnetales and Pro-angiosperms had a common ancestor and the modern angiosperms evolved from the Pro-angiosperms In Polyhyletic lines.

4. Caytoniales-Angiosperms theory (in respect to origin of Angiosperms)

Thomas (1925) suggested that Caytoniales, a small group of angiosperm-like plants, discovered in the Jurassic rocks of Yorkshire (England), might an ancestor of angiosperms.

5. Pteridosperm-Angiosperm theory (in respect to origin of Angiosperms)

Andrews (1947) was of opinion that seed ferns or Pteridosperms, and ancient group of the Palaeozoic, might be the starting point for the angiosperrnic plants

Origin of Dicotyledons

There are two large groups of angiosperms (1) Dicotyledons and (2) Monocotyledons.

The dicots are more important and they are supposed to have originated before the monocotyledons.

It is generally believed and agreed that the dicotyledons have been originated from gymnosperms of a type somewhat different from present day forms of gymnosperms.

Origin of Monocotyledons

This is the subject of great controversy. It is now generally thought that the dicotyledons are more primitive and they have been rise to the monocotyledons. This is also believed, that the monocotyledons were an offshoot of the primitive dicotyledons back in the early Mesozoic era. They are thought to be monophyletic (i.e., of one origin) in their origin. According to another conception the monocotyledons are not monophyletic but polyphyletic in their origin.

References:

• A text book of Botany Angiosperms (1981) B.P. Pandey. first edition, Publishers: S.Chand & Company LTD. Ramnagar, New Delhi-110055
• https://link.springer.com/10.1007/978-3-319-33038-9_60-1
• https://www.biologydiscussion.com/angiosperms/origin-of-angiosperms-with-diagram/30547
• https://palaeoflora.blogspot.com/2019/05/fossils-clocks-and-origin-of-angiosperms.html