Lotus pedunculatus Cav., Greater Bird's-foot-trefoil

Account Summary

Taxonomic uncertainty

There appears to be some taxonomic debate regarding the correct name and status of Greater Bird's-foot-trefoil at present (Feb 2021). Stace (2019) uses the name above and gives L. uliginosus Schkuhr as its synonym. However, he mentions that there is some disagreement as to whether L. uliginosus and L. pedunculatus represent one or two species. If they are separate species, then Stace takes the view that the B & I taxon is L. uliginosus. Sell & Murrell (2009) also regard the B & I plant as L. uliginosus and consider L. pedunculatus Cav. as a distinct, separate species that does not occur in B & I.

Growth form and preferred habitats

This very distinctive, 60 cm or up to 1 m tall, climbing or rather, scrambling on the support of other plants, yellow or orange pea-flower grows in moist grassland and waterside habitats in late summer. It is easily distinguished from the quite similar, but lower-growing, more compact, earlier flowering L. corniculatus (Common Bird's-foot-trefoil) by its hollow stems and calyx teeth recurved on the flower bud (Stace 2019). It is also more shallow-rooted than the latter and has a slender rootstock that produces numerous vegetatively spreading stolons that also help set it apart from L. corniculatus (Clapham et al. 1987).

Until a recently introduced name change, the previously applied Latin species epithet 'uliginosus' (= growing in marshy places) and its English common name Marsh Bird's-foot-trefoil reminded us that this nitrogen-fixing legume occurs in a wide variety of damp to wet grassy habitats, sometimes indeed occurring in stands of great abundance thanks to its vegetative spreading ability (Gilbert-Carter 1964). Locally in Fermanagh these wetland situations include rushy fields, margins of swampy fens or periodically flooded lakeshores, marshy grassy waysides, on damp river banks and in damper hollows in waste ground, a sand pit and on drier parts of bogs, including cut-over bogs.

In terms of soil preferences, L. pedunculatus occupies wet ground of similar nutrient status and range of textures to L. corniculatus, but unlike the latter, as in the Burren in Co Clare (H9), it appears to be completely absent from the most lime-rich soils and, with rare exceptions (ie a couple of cut-over bogs and along parts of the Finn Floods river), it is confined to moderately acid to neutral conditions between pH 4.5 and 6.5 (Webb & Scannell 1983; Sinker et al. 1985). It is largely absent from soils below pH 4.5 (Grime et al. 1988).

While common in periodically or seasonally flooded ground, L. pedunculatus is completely absent from permanently submerged, fully aquatic habitats and also from heavily disturbed sites. L. pedunculatus is the only common legume of wetlands in the B & I flora. The scarcity of legumes on wet ground probably reflects the conflicting demands for a limited oxygen supply during the process of nodule nitrogen-fixation and also in its role in the detoxification of anaerobic conditions around the root in wet soils (Sprent 1984).

On the other hand, Large- or Greater-Bird's-foot-trefoil is much more tolerant of half-shade than L. corniculatus and, since it grows taller and has a larger leaf area, it is the stronger competitor of these two legumes, growing with associated grasses and wet habitat herbs such as Festuca pratensis (Meadow Fescue), Holcus mollis (Creeping Soft-grass), Lychnis flos-cuculi (Ragged-Robin) and Succisa pratensis (Devil's-bit Scabious). The established strategy of L. pedunculatus is described as intermediate between competitor and C-S-R by Grime et al. (1988), on this measure one step up from the more stress-tolerant, less competitive L. corniculatus. It appears to colonise and grow best in relatively infertile, sub-optimal conditions where the growth of potential dominants is restricted.

Flowering reproduction

Flowering in L. pedunculatus is very similar to that of L. corniculatus. Anthesis occurs between June and August, the deep yellow, hermaphrodite, pea flowers being borne 5-15 in number, in axillary cymose heads on long slender peduncles. Like L. corniculatus, the 10-20 mm flowers are protandrous, bee-pollinated and self-incompatible. The weight of the insect visitor is the important factor required to open the flower and squeeze or pump the previously released somewhat sticky pollen out of the tip of the fused keel petals onto the bee's hairy abdomen, rather like a coil of toothpaste. The stigma also protrudes through the keel tip whenever the flower enters the female phase, and an insect revisit then achieves cross-pollination (Proctor & Yeo 1973).

The slender, dry, fruit pods, 15-35 mm in length, slightly longer than in L. corniculatus, mature in a star-like arrangement from August to October. They open in the same manner as in L. corniculatus, by sudden rupture and twist of two valves that explosively eject around 14 seeds from each pod (Grime et al. 1988). Seeds germinate mainly in spring, but a small proportion of them can survive soil burial for at least five years (Thompson et al. 1997). The 1 mm seed is relatively large and although there is no obvious method of its long range dispersal, the species is a quite frequent colonist of vegetation gaps in sufficiently disturbed, damp grassy or muddy waterside sites.

Vegetative reproduction

L. pedunculatus frequently forms substantial clonal patches by growth of numerous spreading stoloniferous shoots produced from the central rootstock of the original plant.

Fermanagh occurrence

Although it is just about a third as frequent and only about half as widespread in Fermanagh as Common Bird's-foot-trefoil, it is almost as widespread as the latter in the eminently suitable, lowland, periodically wet, 'water meadow' habitats around the shores of Upper Lough Erne. L. pedunculatus also flourishes in the eastern half of the VC where, as the tetrad distribution maps illustrate, both these species are much more thinly scattered. There are records of L. pedunculatus in the Fermanagh Flora Database from a total of 150 tetrads, 28.4% of those in the VC.

British and Irish occurrence

The New Atlas map shows that this species is very widespread in Ireland, but much less frequent on the Central Plain and in parts of the extreme west where ± constantly wet, strongly acidic peat bogs predominate. It is well distributed throughout Britain, except in N & NW Scotland and the Highlands, where again, presumably, the soils are just too acid, peaty and cold for it to manage.

Uses

L. pedunculatus contains as much protein and fibre as other common legumes used for fodder, and is or was therefore, a recommended component for cultivation in permanent grassland in periodically moist habitats in Poland (Zimny 1965). It is not used for this purpose in B & I at present.

European and world occurrence

Widely distributed across W, C & S Europe, north to 60°N in Scandinavia and east to 25°E in Ukraine, plus in N Africa and the Canary Isles. It has been spread by man within and beyond this area and is often a casual. It has certainly been introduced to N Fennoscandia and Iceland and to N America, Chile, Tasmania and New Zealand (Hultén & Fries 1986, Map 1250).

Threats

None.

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