Marsh marigold

Marsh marigold (Caltha palustris), the latest addition to our species list, is a member of the buttercup family. While its colour and the shape of its flower seem very familiar, there is a lot about this beautiful plant that is quite unusual.

It is native to the stream margins, marshes and wet woodlands of the whole northern hemisphere. This wide distribution shows that it is an ancient plant; the last time there was a land bridge between Eurasia and North America was 70,000 years ago. The structure of the flower is primitive but it has an adaptability which has eased it into a whole range of ecological niches.

Marsh marigold flowers have no real petals. The bright yellow, pollinator-attracting, landing deck is made of five sepals; sepals are the leaf-like structures that wrap around a flower bud until it opens. Under visible light, the sepals appear to be uniformly bright yellow but under ultraviolet light, which is the part of the spectrum seen by insects, the base of the sepals is almost black. This contrast acts as a signpost that points insect visitors, beetles, bees and flies, to the nectar and pollen.

The plant is very unusual in that it does not separate its male and female organs by putting them on different timetables, flowers or plants. Self-fertilisation does occur but it does not result in fertile seeds. This mechanism, which it seems to share with only one other species, isn’t really understood yet but is an effective way of preventing the loss of genetic variability that self fertilisation inevitably involves.

Fertile marsh marigold seeds float. They contain a spongy material that lets the seed float away from the parent plant; it becomes water-logged quite quickly and strands the seed on a muddy bank not too far downstream. Let’s hope our newly established marsh marigold sends its floating seeds on down the Lambrok.

Conservation Status: Least concern, locally vulnerable to agriculture and drainage


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