Is it a Tweet? Is it a Blog? No its a Bird’s-foot trefoil…but which one?

L.corniculatus (Common Bird’s foot trefoil)

Lotus corniculatus, Common Bird’s-foot trefoil, mentioned in the ‘Peas in the Wilderness’ blog a few weeks ago, also goes by the evocative names Eggs and Bacon, Ham and Eggs, Tomb Thumb, Fingers and Thumbs, Granny’s Toenails, Dutchman’s Clogs etc.  In fact, according to Richard Mabey in his Flora Britannica (1996), there are no fewer than 70 local names!  Some of these refer to the shape of the flowers (medieval slipper or clog-shaped) and some to the colour which, as Mabey puts it, are ‘a delicious suffusion of egg-yolk orange and yellow’.

So why has so much attention been paid to, what is afterall, a rather diminutive albeit very common and widespread plant?  Perhaps its very commonness renders it one of the first flowers we all find when we are first exploring nature and therefore requiring of a name and ending up with very many!

L.pedunculatus (Greater Bird’s-foot trefoil)

Anyway, this is not the only Bird’s-foot Trefoil on campus, the other is Lotus pedunculatus, The Greater Bird’s-foot trefoil.  This is a larger, more striking plant but, by all accounts, it has not been so richly bestowed with vernacular names.  Both these trefoils are quite common in the grassland on Campus.  Both have the yellow pea-flowers characteristic of many members of the Fabaceae.  Both seems to have leaves composed of 5-leaflets but actually, as the common name ‘trefoil’ suggests, there are 3 leaflets but each trefoil leaf has two leaf-like stipules at the junction of the peduncle (leaf stalk) and the stem so the leaves look as though there are 5 leaflets.  So with these similarities, how to tell them apart?

L.pedunculatus on the botanist’s slab

L.pedunculatus, Greater Bird’sfoot trefoil is, not surprisingly given its name, the the larger of the two species (with ascending stems reaching 1 m tall).  The plant can be very hairy but also, unhelpfully for our purposes, quite glabrous, the stem is usually hollow and this can be a useful character, but see below.  Ecologically this is a plant of damp or even wet grassland on campus it is the main species on the damper grasslands on the west-side of the lake.

L.corniculatus

L.corniculatus, Common Bird’s-foot Trefoil, is the smaller of the two species with procumbent or ascending stems reaching only 50 cm tall, the plant is usually glabrous or sparsely hairy, and with a solid stem (though Stace (2010)warns that the non-native L.corniculatus ssp. sativus, widely sown in ‘wildflower’ seed mixes on motorways verges etc, also has a hollow stem, but I have not seen this ssp. on campus).  L.corniculatus is a plant of drier grassland and an campus is widespead but is especially abundant in the sandier grassland on the gentle slopes on the east-side of the lake.  So if we have decent flowering specimens we can use size, stem characters and habitat to help distinguish the two.

Lotus corniculatus (top), L.pedunculatus (bottom)

But when they are not flowering it can be tricky to tell these two apart.  Here, once again, the new vegetative key by John Poland & Eric Clement (2009)  comes to our rescue.  If we take a leaflet from each and ‘htl’ (hold to light), then if we have L.corniculatus we cannot see any secondary veins at all, the leaf is quite opaque.  Whilst in L.peduculatus we clearly see the secondary veins.  A triumph for the good old ‘htl’ technique once again!

About drmgoeswild

Field botanist and ecologist, with a passion for plants and vegetation and teaching and learning (follow me at www.drmgoeswild.com)
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2 Responses to Is it a Tweet? Is it a Blog? No its a Bird’s-foot trefoil…but which one?

  1. Erin says:

    I’ve been pulling my hair out looking at these two species! Do you know if the HTL trick works on dried specimens as well?

  2. HTL does nto work well with herbarium specimens, I’ve not tried it with recently dried specimens.

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