Partridge Pea (Chamaecrista fasciculata). A delicate-looking plant with Mimosa-like leaves that quickly colonizes recently disturbed or burned areas. The cheery yellow flowers can keep coming for months. They are unlike typical pea flowers in being open rather than having the lower petals fused into a keel.
Redbud (Cercis canadensis). A common tree in the forests around Pittsburgh, and also a favorite ornamental in urban and suburban yards. The bright magenta flowers, instead of coming at the ends of branches, pop right out of the wood. They bloom in late April.
Red Clover (Trifolium pratense). This ubiquitous European import grows almost anywhere the grass isn’t mowed too frequently. It came to America as a pasture crop, and soon found that it really liked our open spaces. The leaves usually show a chevron pattern, which distinguishes it from the similar but rarer Alsike Clover (Trifolium hybridum). Red Clover keeps blooming throughout the season.
White Clover (Trifolium repens). It grows in every lawn, but unless you are obsessive about your grass, there is little to object to in this little weed. It is very easy to mow, it never grows very tall even without mowing, and it does the soil good. The flowers are frequently tinged with pink, and of course an occasional leaf grows with four leaflets.
Alsike Clover (Trifolium hybridum). Red Clover (T. pratense) is more common and very similar, and grows in most of the same places. The best way to tell the difference is by the leaves, which in Red Clover usually (but not always) show a chevron pattern but are unmarked in Alsike Clover; and by the color of the flowers, which in Alsike Clover is less magenta and more pale rosy pink, with young white flowers in the center of the head. In fact, it does look like something halfway between Red Clover and White Clover (T. repens), which may account for the specific name hybridus for a plant that is not a hybrid.
White Sweet Clover (Melilotus albus). Imported for fodder, White Sweet Clover and the similar yellow species M. officinalis (almost indistinguishable until the flowers appear) have made themselves at home here to such an extent that some regard them as pests. Nevertheless, as nitrogen-fixers that cattle like to eat, they give us a lot in return for the inconvenience they cause us.
Yellow Sweet Clover (Melilotus officinalis). Hard to tell from White Sweet Clover (M. alba) until they both bloom. When they do bloom, the yellow species reveals sloppier habits; the flower spikes are more ragged than the ones of M. alba, with withering flowers retained for a long time. Nevertheless, the delightful scent is enough to make us forget the slight slovenliness of the presentation. Yellow Sweet Clover grows plentifully along roadsides, and is often one of the first plants to colonize a recently disturbed site.
Birdfoot Trefoil (Lotus corniculatus). This is a plant that seems to be adapted above all to roadsides. It thrives in poor soil and can live happily in gravel, and it stays short enough to laugh at occasional mowing, though it would not survive a mower-obsessed suburbanite’s lawn. It is certainly one of our most decorative roadside weeds. The bright yellow flowers reward a close look: they have thin red stripes on the “standards,” the upper part of the flower.
Black Locust (Robinia pseudoacacia). This tree is ubiquitous in southwestern Pennsylvania, so it may come as some surprise to Pittsburghers that we live at the northern end of a native range that is actually very small, mostly in the Appalachians and foothills. The Black Locust has been much planted elsewhere, however, and may easily naturalize itself. It is in many ways an ideal urban tree: it grows fast, tolerates city conditions with no complaints, and has showy clusters of white pea flowers after most of the other flowering trees have stopped blooming. It does, however, have one serious flaw. Mature specimens are brittle, and can easily drop large branches in storms, crushing cars or bringing down power lines. When your power goes out in a thunderstorm, there’s a very good chance you have a Black Locust to blame.
Showy Tick-Trefoil (Desmodium canadense). Tick-trefoils are mild annoyances to hikers and walkers, but this one is such a beautiful flower that we can easily forgive it. Like all the other tick-trefoils, it has transformed the ordinary legume of the pea family into a fabulously efficient instrument of dispersal. The pod is divided into individual segments that separate easily, and each of them is coated with sticky adhesive hairs. As you pass by the plant, several of those segments stick to your clothes and ride off with you, at least until you notice them. It may be quite a distance: since the seedpods are sticky rather than prickly, you tend not to notice them until you see them. Other tick-trefoils have pretty but inconspicuous little flowers; this one, however, has larger flowers in a dense and showy raceme.
Cow Vetch (Vicia cracca). A European import cultivated for fodder, Cow Vetch tends to be found wherever livestock is nearby. The vines twine through other less decorative weeds, and the beautiful blue-purple flowers light up the edges of fields.
Crown Vetch (Securigera varia). Crown Vetch is often planted to control erosion on hillsides; it also escapes freely and makes a nuisance of itself. But the bicolored flowers are pretty. They come in various shades, including occasionally pure white or lavender.
Everlasting pea (Lathyrus latifolius). A vigorous vine that can take over whole hillsides. It compensates us for the space it takes with a glorious array of flowers in shades from white through deep magenta, often with stripes or bicolor patterns. It’s called “everlasting” because it has flowers like the annual garden sweet pea, but it’s a perennial; thus another common name, “Perennial Sweet Pea.”
Hog Peanut (Amphicarpaea bracteata). A vine that twines its way through the underbrush along creeks and streams, dangling clusters of flowers in white, pink, or purple. These flowers produce seeds, but the vine also grows less showy flowers near the ground that turn into a single underground seed, like a peanut.