Wednesday, 28 May 2014

Sedge mayhem

After the group's last visit to Fosse Meadows, I was checking the characters of some waterside sedges and noticed a glaring discrepancy in the literature. The ligule shape is a distinctive feature in some species, for example, it is obtuse in Carex riparia (Greater Pond-sedge), but acute in Carex acutiformis (Lesser Pond-sedge). Both of these species have 3 stigmas and produce 3-sided nuts, so the ligule character aids identification. Another, more infrequently found species, is Carex acuta (Slender Tufted-sedge) which has 2 stigmas, and produces 2-sided, biconvex nuts, and so, can be easily separated from the previous two species. But, if you haven't got stigmas and ripe nuts, you are forced to rely on vegetative characters. The BSBI handbook Sedges of the British Isles and The Vegetative Key to the British Flora agree that the ligule of C. riparia is obtuse, and that the ligule of C. acutiformis is acute, but they differ about C. acuta. The Sedge Book says its ligule is obtuse, whereas The Vegetative Key says it is acute. The 'Book of Stace' doesn't use ligule characters, so is no help. What to do? Who is right? How does this happen? Perhaps someone out there on the Plant ID course or the Botany for Beginners course can help.


Ligule of Carex acutiformis

Ligule of Carex riparia


Alyson Freeman said...

I have a "Key to Sedges in Hampshire". This says that the ligule in Carex acuta is 4-6 mm, obtuse but cut off at top.

Alyson Freeman said...

The Plant Crib also says obtuse.

Louise Marsh said...

BSBI Sedge Handbook says 4-6mm, obtuse, truncate. But the illustration does not look particularly obtuse or truncate to me. I suggest that we email John Poland and ask him! Maybe LTR Herbarium volunteers and Botany for Beginners students could check specimens when we are all in the Herbarium on Friday? Louise

Chris Hill said...

I thought Carex acuta meant acute ligule? I've checked a specimen today and the ligule is more acute than obtuse.

John Poland said...

The ligule of C. acuta is most definitely acute (and always longer than the leaf width) and closely resembles C. acutiformis. C. riparia always has a v obtuse ligule (often much wider than long).

The best way to separate the three species is not by leaf width but by ligule length and basal sheath colour. Key notes for the 3 spp below:

C. riparia - Ligule obtuse, often much wider than long. Basal sheaths reddish
Carex acutiformis - Ligule acute, always longer than wide. Basal sheaths reddish
Carex acuta - Ligule acute, always longer than wide. Basal sheaths not reddish (usu whitish)

Hope this helps!


Louise Marsh said...

Thanks to John Poland for clarifying - sounds like we all need to look closely at basal sheaths this year. C. acuta has narrower leaf (to 7mm) and rounder stem base than C. acutiformis.
Half-time score: Poland 1: Sedge Key 0