little annual is common on cultivated ground and by roadsides.
The stems are square, the oval leaves are arranged in opposite
pairs, and the flowers, on slender stalks, grow singly from the
axils of the leaves. Red flowers are the rule, but occasionally
they are pink, white or blue. The flowers open only in bright
weather. They are said to close when rain threatens, hence the
old country name "poor man's weather-glass."