Regional botanical differences can be generalised in terms of distinctive groupings of plants. For example in Matthew's oceanic southern biodiversity element, Helianthemum apenninum is restricted to the outcrop of Devonian limestone and to certain areas in the Mendips; Koeleria vallesiana is restricted entirely to the Mendips. Polygala calcarea an important species of the Chalk and Oolitic limestone within the oceanic southern element is more widespread but reaches its highest abundance in the western chalk grasslands and its northern limit on the Oolitic limestone in Rutland.
Twenty-six European species, most of them rare or local plants of calcareous grasslands, are included in Matthew's continental southern element, which in Britain has a markedly southern distribution with the highest concentration of species in south-east England, south of a line joining the Bristol Channel and the Wash. Ophrys fuciflora, 0. purpurea and 0. simia are restricted to the chalk in Kent while 0. sphegodes is found in Kent, Sussex, on the Isle of Wight and on the Jurassic formation in Dorset. More widespread species in this group includes Hippocrepis comosa which extends northwards to the carboniferous limestone in northern England but is only common in the chalk grasslands of southern England. Other species in this group, each with their own special distribution pattern but included in this major south-eastern floristic element are:
- Aceras anthropophorum, Ajuga chamaepitys. Anacamptis pyramidalis, Asperula cynanchica, Blackstonia perfoliata, Buxus sempervirens, Carex humilis, Cephalanthera damasonium, Daphne laureola, Himantoglossum hircinum, Spiranthes spiralis, Trifolium scabrum and Trinia glauca.
Helianthemum canum, Hornungia petraea and Linosyris vulgaris are, however, western species in Britain and found mainly on Carboniferous limestone.
The continental element includes many of the rare species characteristic of the chalk and Oolitic limestone in the south and south-east which are mostly absent from the western Carboniferous limestone. This group includes Pulsatilla vulgaris, Bunium bulbocastanum, Dianthus gratianopolitanus, Hypochaeris maculate, Ophrys insectifera, Orchis militaris, 0. ustulata, Orobanche elatior, Phleum phleoides, Phyteuma tenerum, Carex ericetorum, Senecio integrifolius and Seseli libanotis.
Cirsium acaulon, which is included in this group also occurs on the carboniferous limestone, but it is significant that at the northern limit of its range, in Derbyshire and Yorkshire, it occurs only on south to south-west facing slopes. The northern and sub-montane calcicole element in the flora is well represented below 1,000 ft. on the carboniferous limestone of Northern England, but only one species (Antennaria diolca) in this floristic element reaches the chalk, although the moss Rhytidium rugosum is abundant on the chalky boulder clay in the Breckland. Examples of northern species relatively abundant on the lowland carboniferous limestone of the Pennines, the Peak District and Morecambe Bay are: Viola lutea, Crepis mollis, Trollius europaeus, Prunus padus, Rosa villosa, Draba incana, Cirsium heterophyllum, Geranium sylvaticum, Epipactis atrorubens, Melica nutans, Saxifraga hypnoides and Asplenium viride.
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