In the previous post about early angiosperms, I discussed about many groups that are strongly underrepresented in paleoartistic reconstructions. For this second post on Early Cretaceous flowering plants, we will look at another group of angiosperms that were quite widespread at that time, namely water plants.
Land plants evolved to occupy aquatic environments many times independently. Within angiosperms, different lines have evolved to exploit the aquatic environment, being either emerging aquatics (i.e. with the leaves outside the water), floating-leaves aquatics (i.e. with the leaves floating on the surface of the water), submerged aquatics (where the whole plant is submerged beneath the water surface) and free-floating plants (where the whole plant floats on the surface of the water).
Aquatic plants are often retrieved in the Early Cretaceous record of the flowering plant. Some authors have interepreted this abundance as an evidence of an aquatic origin for angiosperms. However, water plants tend to be rather widespread, and usually grow in sites of deposition, indicating that bias in preservation might explain their abundance.
One group of aquatic plants which seemed to be rather successful during the Cretaceous were relatives of the extant genus Ceratophyllum, a genus of submerged aquatics with very uncertain placement within the Mesangiospermae (i.e., the clade of angiosperms including all extant groups except Amborella, Nymphaeales, and Austrobaileyales). These include Montsechia vidalii, the oldest unequivocal angiosperm macrofossil from the Barremian of Spain (Las Hoyas and Montsec localities) and the Aptian of Italy (Cusano Mutri locality), as well as Pseudoasterophyllites cretaceus from the Cenomanian (early Late Cretaceous) of the Czech Republic. Apart from their unique morphologies, these plants could also suggest a relationship between Ceratophyllum and another typical Cretaceous angiosperm group, the Chloranthaceae.
The members of the order Nymphaeales are also retrieved from the EArly Cretaceous. The most well-preserved come from the Crato Formation in Brazil, and include Pluricarpellatia peltata and Jaguariba wiersemiana. These would have been plant with floating leaves and emerging flowers, like extant Cabombaceae and Nymphaeaceae. In the case of Pluricarpellatia, the flowers do not resemble closely either the large flowers of Nympheaea not the diminutive flowers of Cabomba. Peltate leaves similar to the ones from the extant genus Brasenia are found in the Early Cretaceous of North America. Another potential member of the Nymphaeales is the charcoalified flower Monetianthus mirus, from the Early Cretaceous of Portugal. This extremely diminutive flower (no larger than a few millimeters in its charcoalified form) also differs from the more typical flowers that we associate with the waterlilies.
Many potential members of the Alismatales, a group of monocots that includes many aquatics, are also retrieved in the Early Cretaceous. These include members of the Araceae, which are often emerging aquatics. The Crato formation has Spixiarum kipea, while Orontiophyllum ferreri and Turolospadix bogneri is retrieved in the Early Cretaceous of Spain. Many alismataceous leaves are also found from other Early Cretaceous outcrops, such as the Potomac Group.
Another aquatic plant is the eudicot Nelumbo, a relative of plane trees and proteas. Though it’s superficially quite similar to waterlilies of the family Nymphaeaceae, its leaves are truly peltate (a rare characters in Nymphaeales) and are usually emerging rather than floating. Leaves assigned to Nelumbites, a potential relative of extant Nelumbo, are found in strata from the Late Albian onwards.
Coiffard, C., Mohr, B.A. and Bernardes-de-Oliveira, M.E., 2013. Jaguariba wiersemana gen. nov. et sp. nov., an Early Cretaceous member of crown group Nymphaeales (Nymphaeaceae) from northern Gondwana. Taxon, 62(1), pp.141-151.
Coiffard, C., Mohr, B.A. and Bernardes-de-Oliveira, M.E., 2013. The Early Cretaceous Aroid, Spixiarum kipea gen. et sp. nov., and implications on early dispersal and ecology of basal monocots. Taxon, 62(5), pp.997-1008.
Coiro, M., Doyle, J.A. and Hilton, J., 2019. How deep is the conflict between molecular and fossil evidence on the age of angiosperms?. New Phytologist, 223(1), pp.83-99.
Gomez, B., Daviero-Gomez, V., Coiffard, C., Martín-Closas, C. and Dilcher, D.L., 2015. Montsechia, an ancient aquatic angiosperm. Proceedings of the National Academy of Sciences, 112(35), pp.10985-10988.
Gomez, B., Daviero‐Gomez, V., Coiffard, C., Barral, A., Martín‐Closas, C. and Dilcher, D.L., 2020. Montsechia vidalii from the Barremian of Spain, the earliest known submerged aquatic angiosperm, and its systematic relationship to Ceratophyllum. TAXON, 69(6), pp.1273-1292.
Mohr, B.A., Bernardes-de-Oliveira, M.E. and Taylor, D.W., 2008. Pluricarpellatia, a nymphaealean angiosperm from the Lower Cretaceous of northern Gondwana (Crato Formation, Brazil). Taxon, 57(4), pp.1147-1158.
Sender, L.M., Doyle, J.A., Upchurch Jr, G.R., Villanueva-Amadoz, U. and Diez, J.B., 2019. Leaf and inflorescence evidence for near-basal Araceae and an unexpected diversity of other monocots from the late Early Cretaceous of Spain. Journal of Systematic Palaeontology, 17(15), pp.1313-1346.
Wang, H. and Dilcher, D.L., 2006. Aquatic angiosperms from the Dakota Formation (Albian, Lower Cretaceous), Hoisington III locality, Kansas, USA. International Journal of Plant Sciences, 167(2), pp.385-401.