FAMILIES OF PLANTS 
67 
Wintercress (Barbarea americana). —A smooth perennial 8 to 16 
inches high. The basal leaves are elliptic with wavy margins. They 
may be simple or may have 1 or 2 pairs of small lobes on the 
petiole. The lower stem leaves are similar except that the petiole 
clasps the stem at the base, while the upper stem leaves are more or 
less toothed or lobed. The flowers are yellow. 
Roripa. —Plants of wet places with pinnately-lobed leaves, yellow 
flowers and short, nearly cylindrical pods. The five species found in 
the park may be distinguished as follows: 
1. Plants more or less hairy. 2. 
1. Plants smooth. 3. 
2. Pods shorter than the pedicels—____ Roripa hispida. 
2. Pods longer than the pedicels___ Roripa curvisiliqua. 
3. Plants spreading by underground stems_ Roripa sinuata . 
3. Plants not spreading by underground stems. 4. 
4. Pods about as long as the pedicels_Marshcress ( Roripa palustris). 
4. Pods twice as long as the pedicels.___ Roripa lyrata. 
Charlock ( Brassica arvensis). —This is an introduced weed with 
more or less lobed or toothed leaves and yellow flowers. 
Twinpod ( Physaria didymocarpa) .—Most easily recognized by its 
fruits which consist of two inflated, papery-walled parts joined 
together by the narrow partition and with the persistent style 
between them. The flowers are yellow and quite showy. The plant 
is 4 to 8 inches high and densely white-hairy. 
raise-flax ( Camelina microcarpa) .—An introduced weed with small 
yellow flowers and lance-shaped or arrow-shaped leaves. 
Shepherds-purse ( Capsella bursa-pastoris) is most easily recognized 
by its fruits which are wedge-shaped and deeply notched at the apex. 
It gets its name from the shape of the fruit. A very common weed 
throughout the country. 
Hutchinsia procumbens , which is closely related to the shepherds- 
purse, has also been found in the park. It is a very low, spreading 
plant with elliptic-oblong fruits. 
Pennycress ( Thlaspi arvense) is a smooth, annual herb, 8 to 12 
inches high, with sessile, more or less oblong and irregularly toothed 
leaves. The flowers are small and white. The fruits are very flat, 
nearly circular, broadly winged and deeply notched. Also- known as 
Prenchweed. 
Thlaspi parviflorum differs primarily in the pods which are 
spatula-shaped or oblong. 
Thlaspi coloradense has also been reported as occuring in the park. 
Lepidium apetaluon is a smooth, more or less branched annual, 
4 to 8 inches high, with rather pale leaves. The lower leaves are 
toothed or more or less deeply cut while the upper ones are nearly 
entire. The greenish flowers have no petals and only two stamens. 
The pods are nearly round with a notch at the end. 
