General notes on vegetation and flora
The vegetation of the Rock of Gibraltar is, on the whole, typical Mediterranean in nature. This consists largely of dense scrub of the type known as maquis, but there are other areas of more open, lower scrub known as garigue. However due to the geologic and geographic nature of the Rock there is considerate variation in the type of scrub, and also in the variety of habitats available to plants. Apart from scrub we have extensive sea cliffs, a limited but important rocky shoreline, the unique great sand slopes of the east side, rocky limestone outcrops and fissures, the steppe conditions of Windmill Hill, and the remains of the sandy isthmus which linked Gibraltar to Spain found at North Front Cemetery. Gibraltar is a limestone mountain and so the soil is alkaline. In contrast the mountains in the surrounding area of Spain are largely sandstone and so the soil is more acid. As a result of this there are many species found on the Rock which are rare or not found in the surrounding region. At the same time, the geology of the Rock is similar to that of North Africa, and so there are species common to both regions. All these factors provide a variety of habitats which give rise to an extensive flora, including some plants which are unique to the Rock. The flora of Gibraltar consists of some 530 species, representing almost 90 families and 330 genera. The majority of these are native species, but some of the 530 are species which have been introduced and become naturalised. The principal flowering months are March to May, but flowers may be seen virtually all the year round. However, very few will be out in the summer months (July to August) when very little if any rain falls. Shortly after the first rains in September, new growth quickly becomes evident, and by November, a large number of plants are already visible.
The general appearance in Spring is that of a giant rock garden run wild. It is in this habitat that one can find any of the ten species of wild orchids found on the Rock. These are very rare and difficult to find. The ones found in Gibraltar are Ophrys apifera (Bee Orchid); Ophrys fusca (Brown Bee Orchid); Ophrys lutea (Yellow Bee Orchid); Ophrys tenthredinifera (Sawfly Orchid); Ophrys bombyliflora (Bumblebee Orchid); Ophrys speculum (Mirror Orchid); Gennaria diphylla (Two-leaved Gennaria); Serapias parviflora (Small-flowered Tongue Orchid); Spiranthes spiralis (Autumn Ladies Tresses Orchid); Anacamptis pyramidalis (Pyramidal Orchid).
Sea cliffs and shoreline
This seemingly inhospitable environment, whipped by the Easterlies and South-Westerlies, and lashed by sea spray, provides the ideal habitat for certain plants which are only found close to the sea. These include Limonium emarginatum (Gibraltar Sea Lavender), a plant which is believed to be a North African species, and very rarely found elsewhere in Europe. Other species found here are Crithmum maritimum (Rock Samphire); Suaeda vera (Shrubby Seablite); Limonium sinuatum (Winged Sea Lavender); Asteriscus maritimum (Sea Daisy), actually found throughout the Rock; Frankenia laevis (Sea heath); Senecio bicolor cineraria (Cineraria). Here we also find the very rare Senecio leucanthemifolius (Coastal Ragwort), and Mesembrianthemum crystallinum (Ice Plant).
These are prehistoric consolidated sand dunes, created by wind-blown sands during a time when sea levels were much lower than at present, and sandy plains spread eastward from Gibraltar. This sandy soil provides a unique habitat not only for plants of sandy shores, but for many others. The plants that can survive in this habitat are adapted to withstand salt-laden winds, high temperatures with no cover from the sun, and scarcity of water. Here we find Ononis natrix ramosissima var. gibraltarica (Gibraltar Restharrow), a variety which is unique to Gibraltar. We also find Eryngium maritimum (Sea Holly); Linaria pedunculata (Branched Toadflax); Daucus carota (Wild Carrot); Cyperus capitatus (Sand Sedge); Silene nicaeensis (Sticky Catchfly); Silene littorea (Shore Campion); Medicago marina (Sea Medick); Pancratium maritimum (Sea Holly); Dipcadi serotinum (Brown Bluebell); Euphorbia baelica (Southern Spurge); Cachrys libanotis (Sand Cachrys); Cakile maritima (Sea Rocket); Allium sphaerocephalon (Round-headed Leek); Crucianella maritima (Coastal Crucianella); Delphinium nanum (Violet Larkspur); Dianthus broteri (Fringed Pink); Glaucium flavum (Yellow Horned Poppy); Lotus creticus (Southern Birdsfoot Trefoil); Malcolmia littorea (Silver Sea Stock); Verbascum giganteum (Giant Mullein). A number of these species are also found in North Front Cemetery which is all that is left of the sandy isthmus which separated the Rock from mainland Spain.
At Windmill Hill Flats we find a rather hostile environment: a flat, wind-lashed terrain, with thin, poor stony soil. Despite all this, Windmill Hill is a treasure-house of plant species. In Spring it is a riot of colour, albeit for a brief period. Here we find a number of species which are not found elsewhere on the Rock, including Crocus serotinus salzmannii (Southern Autumn Crocus); Salvia verbenaca (Wild Clary); Echium parviflorum (Small-flowered Bugloss); Plantago serraria (Saw-toothed Plantain); Hedysarum coronarium (Italian Sainfoin); Mantisalca salmantica; Minuartia geniculata (Pink Sandwort); Tetragonolobus purpureus (Winged Asparagus Pea); Lathyrus annuus (Annual Yellow Vetchling). Other important plants found here better than anywhere else on the Rock are Ornithogalum orthophyllum (Star of Bethlehem); Romulea clusiana (Romulea); Gynandriris sisyrinchium (Barbary Nut); Borago officinalis (Borage); Ecballium elaterium (Squirting Cucumber); Echium plantagineum (Purple Viper's Bugloss).
A number of species have been introduced either deliberately or accidentally. Many of these come from countries with a climate similar to that of Gibraltar e.g. South Africa and parts of South and Central America. These have no trouble in settling in and spreading, sometimes to the detriment of native species. Among these plants are Oxalis pes-caprae (Bermuda Buttercup); Agave americana (Century Plant); Carpobrotus edulis (Hottentot Fig) which was introduced in order to stabilise the great eastern sand slopes; Opuntia ficus-indica (Barbary Fig); Freesia refracta (Freesia); Aloe arborescens (Tree Aloe).