Last Saturday Graeme Lyons ran a course for the Freshwater Habitats Trust’s PondNet project at Chailey Common and in his blog[1] highlighted the fact that there were tons of the aquatic liverwort Riccia fluitans in one of the ponds. There was so much of it that it was very easy to compare the terrestrial and aquatic forms of it. This is a new site for this uncommon plant, so a visit was certainly necessary so as to admire the spectacle. There is a huge amount of it there, covering the surface of the pond, and on the muddy edges.

Riccia fluitans habitat at Chailey Common

There really aren’t that many records for Riccia fluitans in the county. The earliest in the database is one of Ted Wallace’s at Pevensey Levels on 11 September 1938, though that is just at the hectad level (TQ60), as are many of the earlier Francis Rose records. The map below shows all the instances of this plant at tetrad level, with the majority being around Amberley area, recorded by Francis Rose, Rod Stern and Howard Matcham, and more recently by Frances Abraham. There are relatively few records from the last couple of years, most notably the population at Knepp recorded by Tom, Sue and Jacqui, so this is a great addition to the list of sites in the county, and is certainly a rare instance of it in the Weald.

Distribution of Riccia fluitans in Sussex

Even so, there are certainly earlier records for this liverwort in the county, as we shall see. William Nicholson’s article ‘The Hepatics of Sussex’ of 1911 notes that it occurs in both vice-counties and is described as “not uncommon”.

As ever, I was curious about the botanical history of this plant, which was named Riccia fluitans by Linnaeus, though he was of course drawing on earlier sources, most notably Dillenius‘ great Historia Muscorum of 1747. In that work it is called Lichenastrum aquaticum fluitans, tenuifolium, furcatum, which certainly describes it quite well, and for good measure Dillenius helpfully provided an English name, the narrow floating forked Lichenastrum, and it is illustrated as number 47 on his Plate 74.

Plate 74 from Historia Muscorum

If we look at the text of Historia Muscorum we can see that it had previously been published in “Cat. Giss.” which was Dillenius’ earlier work Catalogus plantarum sponte circa Gissam nascentium of 1719. That work is a flora of the area around Giessen in Hesse-Darmstadt, where Dillenius studied before moving to England in 1721.

Working back through the references in Linnaeus, Dillenius and others it is interesting to see the network of natural history writers of the first half of the eighteenth century and earlier describing what we now know as Riccia fluitans. In so doing, we can start to get a flavour of pre-Linnean European botany and the astonishing work and erudition on display concerning these small plants as various authors try to make sense of where they might fit into the order of things, sometimes grouping them with the algae.

Pre-Linnean authorities of Riccia fluitans

It is certainly an impressive genealogy, including works by the great French botanist Sébastien Vaillant (1669-1722) who found the plant “around the ponds of the Fontainebleau forest” and on 26 July 1706 in a similar habitat around Franchard. Other early writers who documented it included the Swiss Albrecht von Haller (1708-1777), and the Italian Pier Antonio Micheli (1679-1737), who in his book Nova plantarum genera coined the name Riccia, named after Pietro Francisco Ricci, a Florentine politician and botanist, though he didn’t actually include our plant in that group.

Detail from Plate 19 of Vaillant’s Botanicon Parisiense

The earliest source for our liverwort is in James Petiver‘s list of plants, animals and much else, which was published in 1695 and includes a plant described as Lactuca aquatica tenuifolia segmentis bifidis, which was “Found in a Ditch near Deptford-Dock”. However, in the posthumous edition of John Ray‘s Synopsis methodica stirpium britannicarum (1724) we read “Mr. Manningham and I observed it plentifully in the Ditches about Chichester”, which certainly makes it the first Sussex record, even if we neither know exactly where or when it was found! There haven’t been any recent records in that neck of the woods either. I wonder where they found it?

So, the Chailey population is now the latest in the 300 year history of recording Riccia fluitans in Sussex. It is good to know that people have been poking around in muddy ditches looking for small plants that long.

Riccia fluitans

References

• Dillenius, J.J. (1741) Historia muscorum. Oxford. p.514 <http://biodiversitylibrary.org/page/44581230>
• Linnaeus, C. (1753) Species plantarum. p. 1139 <http://biodiversitylibrary.org/page/359160>
• Micheli, P.A. (1729) Nova plantarum genera. Florence. p. 6 <http://biodiversitylibrary.org/page/33435100>
• Nicholson, W.E. (1911) The hepatics of Sussex. Hastings and East Sussex Naturalist 1(6), 243-292.
• Petiver, J. (1695-1703) Musei Petiveriani. London.
• Ray, J. (1724) Synopsis methodica stirpium britannicarum. London. p. 63 <http://bibdigital.rjb.csic.es/ing/Libro.php?Libro=4837&Pagina=81>
• Vaillant, S. (1727) Botanicon Parisiense. Leiden. p. 98 <http://bibdigital.rjb.csic.es/ing/Libro.php?Libro=5319&Pagina=152>

Note

[1] Graeme Lyons. “The pond life in the acidic pools of Chailey Common” Blog post. The Lyons Den. 16 September 2017. Web. <https://analternativenaturalhistoryofsussex.blogspot.co.uk/2017/09/the-pond-life-in-acidic-pools-of.html>