The yellow flower of the cow wheat blooms in mid-summer. In the ridge area, the common cow wheat is considerably more plentiful than the small cow wheat as it thrives on more rugged terrain while the small cow wheat flourishes in woodland that is dominated by spruce. The species are fairly similar, but they are easy to distinguish from each other. The flowers of the common cow wheat are usually pale yellow, while the flowers of the small cow wheat are clearly orange-tinged. Another good way to tell the difference is that the lower lip curves downwards.
Common cow wheat melampyrum pratense
Small cow wheat melampyrum sylvaticum
Photos: Jyrki Oja
Cow wheat are an unusual forest plant because they last a single year while most are long-lived or live for at least two years.
As cow wheat is a hemiparasite; it uses a host’s plant’s roots to reproduce, i.e. it takes nutrients from another plant. Its seeds will grow a few with the aid of their own store of nutrients but they will seek out other roots and when one is encountered it will secrete an enzyme that dissolves the root stem of the host. The cow wheat then absorbs the host’s nitrogen and phosphorus compounds, which it needs to blossom. The host plant can be almost any species, but shrubs, pine and spruce are preferred.
Older generations knew it by the name voiheinä (butter hay), almost certainly because their flowers are the traditional colour of butter and maybe because livestock grazing in the forests gladly ate them.