There’s a small boggy area just north of the west side meadow below the tree-lined ridge. A few years ago there was enough standing water here for ducks to splash around in. Then the engineers got busy and drained it, but it’s still soft, spongy and treacherous underfoot. My careful venture into the midst of it yesterday evening was rewarded with a view of these small yellow flowers growing close to the ground. I think they’re Birdsfoot Trefoil, Lotus corniculatus.
Wikipedia says the plant can be used as cattle feed, and may have some medicinal uses:
It is used in agriculture as a forage plant, grown for pasture, hay, and silage. Taller growing cultivars have been developed for this. It may be used as an alternative to alfalfa in poor soils. It has become an invasive species in some regions of North America and Australia.
A double flowered variety is grown as an ornamental plant. The plant is an important nectar source for many insects and is also used as a larval food plant by many species of Lepidoptera such as Six-spot Burnet. It is regularly included as a component of wildflower mixes in Europe.
Fresh birdsfoot trefoil contains cyanogenic glycosides, which releases small amounts of hydrogen cyanide when macerated. This is however not normally poisonous to humans, as the dose is very low, and the metabolization of cyanide is relatively quick. Condensed Tannins are also present in Lotus Corniculatus, which has been known to increase the protein absorption of the small intestine. Used in an infusion to avoid the creation of hydrogen cyanide this plant can be used as a sedative 
But the US Department of Agriculture’s Forest Service features lotus corniculatus as one of its “Weeds of the Week.” That would be in line with most of the other plants that grow wild in the park. However, we fans of the park have learned to appreciate just about anything that flourishes and flowers here, even if some authorities label it with the w-word.