NORTHERN ROCK-CRESS

Arabidopsis petraea

(Formerly: Arabis petraea)
Cabbage Family [Brassicaceae]

month8jun month8june month8jul month8july month8aug

status
statusZnative
flower
flower8white
flower
flower8mauve
inner
inner8yellow
morph
morph8actino
petals
petalsZ4
stem
stem8round
rarity
rarityZscarce
sex
sexZbisexual

9th June 2018, Keen of Hamar, Shetland. Photo: © Jill Stevens
With basal leaves long-stalked and somewhat similar to those of Rue-Leaved Saxifrage, but pinnate, having one or two more pairs of side-lobes. Leaves here dark-green, red when suffering from stress, and fawn when dying. The rhizome branches; another set of basal leaves (this time beetroot coloured) are in a rocky nook at 2 O'clock from the plant. The stem leaves are oval and sparse and the stem is also suffering from stress, being reddish brown. The basal leaves can look quite different to these, but I have assurance that these specimens are indeed Northern Rock-cress. They just lack the other shape of basal leaves which have a long rectangular end with various shapes of triangular teeth common to those specimens found on mainland Britain.


9th June 2018, Keen of Hamar, Shetland. Photo: © Jill Stevens
Flowers with 4 petals, slightly zygomorphically arranged in opposing pairs. White to purplish flowers. Sepal teeth long and well-rounded at their ends and very loosely cupping the flower.


9th June 2018, Keen of Hamar, Shetland. Photo: © Jill Stevens
With 4 anthers arranged in a rectangle, and another two lower down at both extremities of the rectangle and half-hidden in the depths of the flower; making 6 anthers in all, and one central style with discoidal stigma. The flowers are quite similar to those of Garden Arabis. They can be white through pink to purplish.


9th June 2018, Keen of Hamar, Shetland. Photo: © Jill Stevens
The seed pods. [The balled-up dead plant bottom RH corner is not part of this plant. It could be Thrift, which is also found on Keen of Hamar]


Related to : Thale Cress (Arabidopsis thaliana) and to Sand Rock-cress (Arabidopsis arenosa)

The plants growing on Serpentinic Rock on the Keen of Hamar, on Unst, Shetlands usually have differing characteristics to the same species which occur much further south on mainland Britain. They may be stunted and/or their leaves take on a differing form and shape (as in the specimens on this page) and various other differences. This is not fully understood but is most certainly due to a combination of features such as the much more inclement weather so far up North, the really rather rare serpentinic soil upon which they grow, plus the elementary composition of that soil - deficient in some minerals with an excess of other elements including some heavy metals.

See Keen of Hamar or Serpentinic Rocks for some reasons why plants groing on the Keen of Hamer often differ in form to the same species growing on mainland Britain. The fact that Thrift (a renown metallophyte which is able to sequester many differing heavy metals and stash them out of harms way) also grows on the Keen of Hamer is surely testament to the protection afforded by heavy metal concentrations if the plant has some mechanism for dealing with the heavy elements.

Northern Rock-cress is native and grows on rocky-ledges of mountains, mountain crevices and rocky slopes in North west Wales, North Central Scotland and extremely locally in Ireland.


  Arabidopsis petraea  ⇐ Global Aspect ⇒ Brassicaceae  

Distribution
 family8Cabbage family8Brassicaceae

 BSBI maps
genus8Arabidopsis
Arabidopsis
(Thale Cresses)

NORTHERN ROCK-CRESS

Arabidopsis petraea

(Formerly: Arabis petraea)
Cabbage Family [Brassicaceae]