Back to Basics: The Basal Angiosperms

Darwin's 'abominable mystery’ describes the rapid expansion of the Angiosperms seen in the fossil record. The event conflicted with Darwin's belief that evolution was slow and gradual, and the massive expansion event of flowering plants across the globe puzzled him. 

Fig. 1 Expansion of the Angiosperms (purple) from 120 Ma

The Angiosperms are the most successful lineage of Land Plants, with around 400,000 species in almost all habitats. Their massive expansion came about during the Lower Cretaceous, around 120 Million years ago (Ma) (Fig. 1).

But where did they come from?

The closest living ancestor of all angiosperms has been a controversial topic for many years, with many different plant groups suggested as the top contenders.

In the late 1990s, the Angiosperm Phylogeny Group (APG), a huge collaboration of many scientists across the globe, worked to reveal the relationship of the majority of the Flowering Plant Families (i.e. Angiosperms) by sequencing certain genes from many different plants. This revealed that one species named Amborella (which only occurs in New Caledonia, Australia) is sister to all Angiosperms, and therefore most closely related to the ancestor of all Angiosperms.

Fig. 2 Basic evolutionary tree of Angiosperms. The basal Angiosperms include the ANA clade in the red box.

The Order Nymphaeales is thought to be the next closely related group of plants to Amborella. These two taxa, plus another order with the lovely name Austrobaileyales (say that after a few drinks!) from what is know as the ANA clade.

Although we don’t have Amborella or the Austrobaileyales in Ireland, we are privileged to have two species of the family Nymphaeaceae (within the Nymphaeales). There are only 50 species of belonging to this family, but they have managed to spread themselves around, and are found in many water systems. 

Distribution of Nymphaea alba 
in the British Isles

Nymphaea alba flowers and leaves
commons.wikipedia.org

The species found in Ireland are Nymphaea alba and Nuphar lutea, also known as water-lillies. Both of our native water-lilies inhabit still, clean water, and are easily recognizable by their floating, peltate leaves, and their beautiful, large flowers which can be seen from May to July.

Nymphaea alba (Bacán bán) named for its pure white flowers, is widespread all over Europe, and within Ireland they are more commonly found in the West. . The long stalks that hold up the peltate leaf blade is not a stem, but the pedicel of the leaf. The plants are anchored to the mud by the stem which lies horizontal on the bottom, and have many adventitious roots that penetrate the mud, holding the stem in place.

Distribution of Nuphar lutea
in the British Isles

Nuphar lutea flower
and leaves.
commons.wikipedia.org

Nuphar lutea (Cabhán abhann) or the yellow water-lily, is much more widespread globally, as it can be found in the temperate parts of the Northern Hemisphere.
In Ireland they are frequent from Lough Neagh in Northern Ireland down to County Clare, but rarer in the South and East Ireland. Apart from the yellow flower heads, these plants are distinguishable from Nymphaea as their flowers are on elongated peduncles that stick out, away from the water surface. 

A family that is quite rare in Ireland is Ceratophyllaceae, aka the Hornworts. Although they are not part of the Nymphaeales, or even the ANA clade, I find them interesting as they seem to cause a bit of trouble with many taxonomists. 

In APG III (2009) they state that 'the molecular evidence that Ceratophyllaceae are sister to the eudicots is becoming clearer', but 'they are morphologically divergent from their putative closest relatives'. The reason I have put them in with this post is because they are basal, aquatic, like our water-lilies, but also because they are very rare.

Ceratophyllum demersum. Image from
http://www.biolib.cz/en/taxonimage/id65312/

Ireland has two species: Ceratophyllum demersum which has only been recorded less than 15 times over the last 10 years. Although it is rare in the British Isles, it has become a major invasive species in New Zealand.

C. submersum has only been recently recorded in two locations in Ireland, once in Co. Down and once in Co. Wexford. It may be overlooked elsewhere, so get a-lookin' in some pools!