Monday, June 3, 2013

Yellow roses

The chalk grassland of the White Cliffs is awash with wildflowers in summer. One of those flowers, characteristic of chalk grassland, is common rock rose; the beautiful Helianthemum nummularium.

Rock rose, Helianthemum nummularium

It's not a rose of course. The common name 'rock rose' is  misleading as these dainty flowers are unrelated to roses, but are in the Cistaceae family. Common rock rose has 5 petals, crumply and crinkly like tissue-paper Cistus flowers.

The dazzling little yellow flowers of rock-rose are on display from late spring to late summer. It's also a very small evergreen shrub so sharp-eyes will discover its leaves even in mid-winter. It prefers to grow on chalky ground, in the sun, especially cliffs and rocks, so the White Cliffs of Dover are nigh on perfect habitat.

Rock rose, Helianthemum nummularium

Not only is it gorgeous for us to look at, its long flowering period makes it an important nectar source for bees. It's the food plant for some species of butterfly; brown argus, green hairstreak and silver-studded blue (the latter being very rare). Larval food plants of UK butterflies are listed here.

Green hairstreak. Copyright Gail Hampshire.
Used under a CC-BY 2.0 licence. Original on Flickr here.

Silver-studded blue. Copyright Gail Hampshire
Used under a CC-BY 2.0 licence. Original on Flickr here.

Rock rose, Helianthemum nummularium, 

The photo above shows the back of the flower with the 5 sepals characteristic of the Cistaceae family; 2 little outer green ones and 3 larger, inner stripey ones.

Helianthemum is from the Greek helios, sun and anthemon, flower, so sun-flower. Nummularium is derived from the Latin 'nummulus', the diminutive of 'coin-shaped'. The bright yellow flowers do resemble little gold coins in the grass.

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