2000/06/01 by Stephen G. Compton, Roger S. Key · 1 citation
Agricultural and Biological Sciences · #Plant Ecology and Taxonomy Studies #Botany, Ecology, and Taxonomy Studies #Plant Taxonomy and Phylogenetics
paper · pdf · doi:10.1046/j.1365-2745.2000.00477.x
openalex publication_date 2000/06/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/06/22
A biennial or short-lived perennial herb. Stem up to 1.3 m high, pubescent, hairs appressed. Leaves pinnatifid-lyrate, up to about 45 cm in length and 13 cm in breadth, pubescent with ascending hairs. Flowering stems erect, branched, woody below in older plants. Inflorescence loose racemose, with generally fewer than 10 flowers open simultaneously. Petals large, up to 9 mm across and 10.5 mm long, with a 9.5-mm claw; petals and petal veins yellow. Sepals up to 8 mm long, erect until after anthesis, pubescent, yellow, with yellow-green veins. Pedicel ascending, mainly between 25 and 45° from vertical when bearing buds, and between 45 and 90° from vertical when flowers are open; siliqua mainly straight. Distal end of valves obtuse. Beak straight to curved; length of mature siliqua up to 60 mm, with beak up to 20 mm. Valves dehiscent, beak indehiscent. Seed length 1.2–1.9 mm. Mean air-dry mass of the seed is 1.52 mg (n = 20, range 0.85–2.53 mg). Tap root slender for its length. Smell strong, cabbage-like. Other vegetative and floral characteristics are given in Table 1. No recorded variation in flower colour or other discrete phenological characters, but some variation in flower size has been noted (Leadley & Heywood 1990). Coincya (Brassicaceae) was synonymised with Rhynchosinapis by Leadley & Heywood (1990) and currently includes six species and several subspecies. It is distinguished from Brassica and Sinapis by the combination of the upper stem leaves not clasping the stem, valves of the fruit having several prominent parallel veins, a slightly flattened beak, large petals and erect sepals (Rich 1991; Stace 1997). In contrast to these genera, Coincya is probably monophyletic and distantly related to other genera in the subtribe Brassicinae (Warwick & Black 1993). There are, however, few clear morphological characters (Leadley & Heywood 1990) and chloroplast DNA characters (Warwick & Black 1993) to distinguish the species belonging to Coincya. Coincya has a western European distribution, with a concentration of taxa in the Iberian Peninsula. Five of the six species have very local distributions and most are regarded by Leadley & Heywood (1990) as being relict taxa. The majority of the species are associated with either rocky slopes or maritime sands, though others occur in alpine meadows and ruderal habitats. Coincya wrightii (Lundy cabbage) –‘loose and sprawling, but bright in hue’ (Gosse 1874) – is a native British species endemic to the island of Lundy in the Bristol Channel, where it is confined to a 2500-m length of coastline. Coincya wrightii was first distinguished by O.E. Schulz (as Brassicella wrightii) in a publication by Wright (1936). Previously it was considered as a form of Coincya monensis (L.) W. Greuter & Burdet or Brassica oleracea L. The widely distributed and highly variable C. monensis differs from C. wrightii in longevity (it is generally annual), basal leaf shape and the extent of stem hairiness (it is generally less hairy) (Leadley & Heywood 1990). Lundy is situated in the Bristol Channel, some 18 km from Hartland Point, Devon (Fig. 1). It comprises a central plateau bounded by cliffs and steeply sloping ‘sidelands’, with a total area of around 430 ha and a highest point of 141 m a.s.l. Coincya wrightii has a current altitudinal range of around 2–120 m, from the splash zone to the top of the cliffs. It extends inland to a maximum of around 300 m in Millcombe. The distribution and abundance of Coincya wrightii on Lundy in 1997, mapped on a 100-m grid. Coincya wrightii occurs mainly along the southern and central parts of the eastern coast of Lundy, with a few plants also in Lametry Bay on the south coast (Fig. 1). In 1997, it was present within a rectangular area extending 2500 m N-S and 600 m E-W. The plant is widely distributed within this area, in 1997 being present in 60% of the 100 × 100 m squares which include at least some land. Early records (Gosse 1874; Wright 1936) implied that the distribution of Coincya wrightii was limited to the loose, weakly metamorphosed Devonian slates that form the extreme south-east of the island, which are replaced by Eocene granites from Ladies' Beach northwards. More recent records (Marren 1972; Irving 1984; Farrell 1993) have shown that plants occur as far north as Knight's Templar Rock and in some recent years more individuals were present on the granites than the slates. The apparent range expansion this century is probably not genuine, as most of the populations in the northern part of its range are on near-vertical cliffs that are partly or wholly hidden from above. Small temporary populations appear at the edge of the plateau and on some of the more gently sloping sidelands. Stock exclusion experiments have confirmed that these populations fail to flower owing to vertebrate grazing pressure (S.G. Compton & R.S. Key, personal observation). Stock have been maintained on the island for centuries, so this does not imply any recent contraction in range. While the range of the plants has been relatively stable during recent years, the size of the populations has apparently fluctuated widely, from a recorded low of 324 plants in flower in 1978 to over 10 000 in 1998 (Cassidi 1980; S.G. Compton, R.S. Key & R.J.D. Key, personal observations). Surveys have varied in intensity, however, and it seems likely that the earlier counts missed many plants growing in the more inaccessible locations. Furthermore, the proportion of plants that flower varies considerably between years, and counts based only on plants in flower can be misleading. The climate of Lundy is mild, with warmer winters and cooler summers than the mainland, reflecting its westerly and maritime location. Annual rainfall averaged 1150 mm during the period 1971–92 with the lowest monthly average of 52.2 mm in July (Gibson 1993). Coincya wrightii occurs typically in exposed, open situations, but persists under moderate shade from trees, Ulex europaeus, Prunus spinosa and the fern Pteridium aquilinum. It is found mainly on bays cut into the sea cliffs, but also colonizes steeply sloping sidelands, rocky outcrops and the sides of well-vegetated gulleys, most prominently in Millcombe. It rapidly colonizes land-slips, which are a regular feature on the slates in the south of its range. Coincya wrightii is favoured by, but is not restricted to, south- and east-facing slopes. The northern limit of the plant does not correspond closely with changes in geology, as its range extends throughout the first and slightly into the second of the two granite types distinguished by Dollar (1941). Differences between the granites are considered to be minor (Edmonds et al. 1979; Thorpe et al. 1990) and changes in coastal topography towards the north of the island, leading to easier access by grazing mammals, may be the factor limiting the distribution of the plant. Some apparently suitable areas nonetheless remain uncolonized. In the south, the factors limiting its distribution appear more clear cut, as exposure increases strikingly away from the east coast, which is sheltered from the Atlantic gales, and this is associated with general changes in the vegetation on the cliffs. Coincya wrightii typically occurs on moderate to steep slopes, where it is rarely subject to waterlogging. Soils on Lundy are well-drained, loamy podzols (Dawes 1979). They are characterized by the Soil Survey of England and Wales as belonging to the Moretonhampstead Series in the south, the Moorgate Association in the north and the Hexworthy Series on the cliffs (Dawes 1979; Edmonds et al. 1979). The soils show considerable local variation in acidity, with pH values ranging from 4.9 to 6.2 on the slates and 2.9 (beneath Rhododendron ponticum) to 6.5 on the granite (S. Richardson, personal communication). Soil nitrate values are highly variable, with no clear relationship to underlying strata, ranging from less than 1 to 140 mg L−1 soil filtrate (based on soil samples mixed with an equal volume of water, Richardson et al. 1998). A series of 25 irregularly shaped vegetation plots, averaging around 64 m2 in area, and sited so as to include as far as possible the full range of vegetation types occupied by the plant, contained 82 associated vascular plant species. Rubus fruticosus, Sedum anglicum, Teucrium scorodonia and Umbilicus rupestris were the most frequently occurring associates, with many of the other species recorded only rarely and/or at low cover values (Table 2). The association with R. fruticosus is likely to reflect the protection from grazing mammals afforded by its prickles. Within its narrow coastal range, the plant appears to occupy almost the full range of plant communities present. A classification of the 25 plots using Ward's Method (performed by SPSS 6.1; SPSS Inc., Chicago, USA) distinguished three main groupings (Fig. 2). A broadly similar classification was obtained when average linkage (between groups) was employed. The first group of vegetation plots distinguished by the classification (between plots 1 and 8 in Fig. 2) comprises communities found on inland granite outcrops, sea cliffs and a large, active rockslide on the slates above Victoria Beach. It is characterized by large areas of bare substrate, and a high species richness (Table 3). The second group of plots (between 9 and 17 in Fig. 2) include more heavily vegetated sea and quarry cliffs, and the deep valley of Millcombe. The highest average cover values of Coincya wrightii are recorded from this vegetation group, together with a relatively small coverage by bare ground. Pteridium aquilinum and the climbers Lonicera periclymenum and Hedera helix are also frequent. The third group of plots (between 18 and 25 in Fig. 2) were situated on the slate cliffs in the south of the plant's range, the relatively gently sloping sidelands, and a hillock dominated by Ulex europaeus. Coincya wrightii was never abundant in these plots, where grass cover was consistently 50% or higher. A classification of the plant communities on Lundy that include Coincya wrightii. The cliff communities with Coincya wrightii do not figure in the National Vegetation Classification (Rodwell 1993–2000), but fit adequately into the coastal extremes of communities W24 (Rubus fruticosus–Holcus lanatus underscrub) and W25 (Pteridium aquilinum–Rubus fruticosus underscrub), particularly W25b, the Teucrium scorodonia subcommunity. MC12a Festuca rubra–Hyacinthoides nonscripta cliff bluebell communities also appear to be represented (A.J.C. Malloch, personal communication). The communities containing Coincya wrightii are dynamic in terms of their turnover of species and changes in total vegetation cover. This is particularly true of the early successional communities developing on unstable shales (Fig. 3), and granite cliffs (Fig. 4), but is also evident in gorse-dominated inland populations (Fig. 5). Vegetation changes on the 1994 landslip above Victoria Beach: (a) changes in late-May/early-June percentage cover (dark area vegetated) between 1994 and 1997; and (b) percentage cover for different plant species within the vegetated area, based on visual estimates for each year; C = Coincya wrightii, G = combined grass species, D = Digitalis purpurea, Se = Sedum anglicum, T = Teucrium scorodonia, Sc = Scrophularia scorodonia, n values indicate the remaining number of species present. Vegetation changes on granite cliffs at Quarry Bay: (a) changes in the late-May/early-June percentage cover (dark area vegetated) between 1994 and 1997; and (b) percentage cover for different plant species within the vegetated area, based on visual estimates for each year; C =Coincya wrightii, G = combined grass species, R =Rubus fruticosus, n values indicate the remaining species present. Vegetation changes on an inland hillock just north of Millcombe: (a) changes in the late-May/early-June percentage cover (dark area vegetated) between 1994 and 1997; and (b) percentage cover for different plant species within the vegetated area, based on visual estimates for each year; C =Coincya wrightii, G = combined grass species, U =Ulex europaeus, n values indicate the remaining species present. Coincya wrightii is fairly tolerant of competition, persisting under Ulex europaeus and even seeding into deep litter beneath stands of Pteridium aquilinum. Seeding experiments have, however, shown that it cannot persist in the dense sward which characterizes some less steep areas of the sidelands. It also does not survive under the alien shrub Rhododendron ponticum, which poses a considerable threat to its survival. Rhododendron ponticum is increasing its range on the eastern sidelands of the island, where it forms almost monospecific stands and is colonizing the previously Pteridium aquilinum-covered sidelands, occupying crevices in rocky outcrops, and spreading down onto the cliff face from the upper sections of the sea cliff. Without control, it appears capable of encompassing most, if not all, of the habitat range of Coincya wrightii (Compton & Key 1998; Compton et al. 1998, 1999). Randall (1978) considered that Coincya wrightii occurs in areas ‘which are mostly inaccessible to grazing animals’, a conclusion borne out by recent surveys and stock exclosures, which have shown that ‘sink’ populations are present on the gentler slopes of the sidelands where reproduction is only possible once grazers are excluded. Some protection is afforded to plants growing within dense Rubus fruticosus, which can provide effective barriers to sheep and goats. There is no record of regular human utilization for food; the leaves are overpoweringly cabbage-scented. Most visitors pay no attention to the plant, despite its proximity to the main road on the island, and much of the population is found on steep and often inaccessible cliffs. Picking or uprooting is therefore not considered as a problem. The plant is rarely solitary, with populations typically comprising scattered individuals separated from their nearest neighbours by less than 5 m, and some plants contiguous. The most isolated individuals are found in atypical situations, such as on a fallen tree trunk in Millcombe, or on a rock exposure surrounded by a large, closed rhododendron canopy. There is no simple relationship between abundance, gregariousness and vegetation succession. In late May 1997, an early successional population on a 1994 land slip occupied 6.0% of the 252 0.25 m2 squares in an 18 × 14 grid. A mean of 1.27 ± 0.46 (SD) plants were present per occupied square (range = 1–2 plants, n = 19 plants of which 17 were flowering or had flowered). In an 8 × 8 × 0.25 m2 grid positioned on a more mature sward nearby, 40.0% of the 0.25 m2 squares were occupied. There was a mean of 2.09 ± 1.31 plants in those 0.25 m2 grid squares that were occupied (range = 0–5, n = 48 plants of which 24 were in flower). Subpopulations are generally separated by less than 100 m (Fig. 1), with the largest break around 400 m, separating the most northerly 10% or so of the plants from the remainder. The tallest individuals are found in the sheltered conditions of Millcombe, where they can reach over 1.3 m in height; they are shorter on the sea cliffs and inland rocky outcrops, but the plants are not markedly stunted even in the most exposed situations. Numbers of flowers produced are correlated with overall plant size, with some individuals flowering when less than 30 cm tall. Soil disturbances favour Coincya wrightii and it is an effective coloniser of open ground, which is produced and maintained within its range by the instability of the substrate in the south, and the steepness of the granite outcrops and sea cliffs further north. Rabbits, larger grazers, streams and human activities also contribute to small-scale sward disturbance. One large-scale land slippage, above Victoria Beach in May 1994, was immediately colonized by C. wrightii which had survived being carried down with the soil and rocks. Seedlings were already present by September the same year. Continuing disturbance in this area through to 1998 severely inhibited plant colonization, and C. wrightii has remained one of the most numerous colonists. A slightly smaller slippage occurred approximately 100 m away in March 1997, and C. wrightii was again amongst the first species to colonize. Lundy has a mild, maritime climate, where frosts are typically infrequent and mild, yet Coincya wrightii growing in gardens on the mainland can survive frosts as severe as − 15 °C. Adult plants appear to be drought tolerant, although the severe drought of 1995 did coincide with high late-summer mortality rates among mature plants in Millcombe. The mortalities nonetheless occurred only after a period of intense flowering activity had been completed, and may have been the result of the latter, rather than drought per se. Subsequent recruitment of young plants was exceptionally high, suggesting that drought may favour C. wrightii through reduced competition. Consistent with this pattern, high population levels were recorded in 1993, a year preceded by several warm and dry summers. Long slender tap root extending to almost 2 m. Stem erect, branched above, woody towards base, sparse to densely pubescent, covered with simple appressed hairs. Leaves deeply pinnatifid-lyrate with sinuations increasing in depth towards the petiole, the lower leaves broadly ovate with broadly triangular terminal lobe and rectangular lower lobes, the margins broadly with the upper leaves broadly deeply into triangular to with smaller often with an of to separated from the main to the on the lower of leaves average (range n = on the upper (range n = of the of plants from Lundy by of the present were some but no or were personal communication). also in years when conditions are can reach at least years by seed = as in most for Coincya wrightii. and seed has been in Iberian et al. Flowering typically in in early and persists at low levels through to September or flowering is in small plants flowering for the first are recorded between and Flowering within is typically few flowers being produced to the first between is is not but most abundant in Some plants flowers the but S.G. Compton, but Leadley & Heywood 1990). of the have shorter the top of the the same as the and × 2) have with which the petals and as they The shorter mature slightly The flowers are bright yellow, with a for by the and of each petal at The is and are with The are by a of about 8 mm, which to very small or those with the flower sepals at the and the sepals from each access to the from the are from Lundy, but a of other as as and and the flowers and are (Table Wright that the of were the are by far the most floral often covered in but they may not be They also on the petals and flower buds, as as and are minor of such as Leadley & Heywood (1990) that two other and also contribute to but species appears to the flowers Key & S.G. Compton, observations). with that may also be & The range of C. wrightii does not with any and no are It can be with other the being & 1972; Leadley & Heywood 1990). plants can several each containing on average 18 (Table 1). of the in the where up to may be with a maximum of in the The siliqua is dehiscent, the some from the plant, those in the beak are only as the fruit regarded this fruit as seed in and and a expansion in the size of the beak among Iberian taxa to the in Coincya wrightii) in terms of the of a more Seed can 30 m, based on the of in the soil throughout the 60 m of separating populations of C. wrightii on inland and sea cliffs personal communication). of are to the and to some of the as they break They may the more widely, if they do not those that they The of across the sea seems given that the and in for up to can remain (Rich 1999). from plants in July did not immediately of less than was recorded by when were on at In a of by was recorded for by from the soil in and maintained at 20 °C. is not for Soil indicate that is under suitable with around of those that so within and over within at 20 (Fig. R. personal communication). The longevity of in the soil can be at least years, based on records the of an isolated group of plants in 1997 in an area where no flowering had occurred in the for a seed is by in soil samples from areas where no flowering had occurred for several years (Table 5). Coincya wrightii rates ± at 20 ± 2 °C. et al. n = total number of = is in Fig. are around the as in other Coincya species (Leadley & Heywood 1990). in Coincya wrightii. to 14 and after and are currently on the island and populations of and are present. may Lundy but this is confirmed only for and its small area of distribution, Coincya wrightii a large and (Table Furthermore, and in the British C. wrightii is the only for an endemic species, the Lundy 1998). It is also the main of two other of the Lundy and the Lundy currently regarded as a of mortalities owing to have not been but are generally high, and plants are by A of leaves on 10 plants in May of which leaf by the of and had by the of and had by The may have the most on the reproduction of the plant, as it around of the in in per of the also of by noted levels of leaf and fruit in the relatively sheltered areas around Millcombe, but so far as is the more are distributed throughout the range of their and the of seed found no between the Millcombe, Quarry Bay and Victoria Beach populations and are similar in to those produced by and leaf and on seed plants were present just above high at Victoria Beach in 1994 and The that Coincya wrightii was to Lundy by from the was by (1936). The temporary of the island by the in the late with their have been one in which the plant have been is no that they occupied Lundy, to the of the to up the island possible of was the island as a and in the century to the of human is the of records from and the of taxa apparently associated with the plant. have been to the plant's association with Lundy It is of that it was the of the which Wright that the plants were a species, confirmed by O.E. Schulz personal communication). It seems that Coincya wrightii in on Lundy from a more mainland as it is not to the British form of C. the only native to Lundy an island as sea levels and was an 10 its current area about years & Wright that the and of Lundy are with no of any effective land to the Leadley & Heywood (1990) considered C. wrightii to be a relict and that the very climate of Lundy have the island to as a during Lundy not have from the of the Atlantic during the period and may have been sea in the area, of the plant highly of Lundy may have been from populations in the Iberian as Coincya has a concentration of taxa in that area, and Leadley & Heywood (1990) noted that C. wrightii and with forms of C. monensis in that are among other The plant may have been after the of the at which with of along the coast of The of Coincya wrightii is and it is under 8 of the and the Most of its distribution within a of with its it is in the There is of soil to streams the south-east of the island, owing to but only a small proportion of the population is found in these areas et al. 1998). have been for the of Lundy and its associated and for the of Rhododendron ponticum on Lundy (Compton & Key 1998; Compton et al. 1998). to Key, Farrell and and to and for their during the of and to the other of Lundy for possible and with was by and the on and Edmonds with morphological to for and during the of this on Lundy was possible by the and of the