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Phyteuma spicatum L.

2002; Wiley; Volume: 90; Issue: 3 Linguagem: Inglês

10.1046/j.1365-2745.2002.00671.x

1365-2745

Belinda R. Wheeler, Michael J. Hutchings,

Bryophyte Studies and Records

A polycarpic, glabrous, perennial hemicryptophyte. Flowering shoots erect, 25–95 cm, produced annually from the axils of cataphyllary (scale-like) leaves on an enlarged primary root. Root green or reddish externally, becoming brown with age, growing vertically within the soil, or horizontally just beneath the soil surface. Phyteuma spicatum is heterophyllous, producing simple leaves. Basal rosettes usually consist of 2–6 petiolate leaves, 25–40 mm wide and 50–80 mm long. Petioles 40–150 mm long. Blades ovate-cordate and singly or doubly serrate or crenate and obtuse. Rosette leaves present at anthesis. Cauline leaves inserted alternately on the stem. Lower cauline leaves similar in form to basal leaves. Upper cauline leaves with rounded or cuneate base, becoming progressively smaller up the stem towards the inflorescence. Blade length : width ratio increases from the lowest to the highest cauline leaves. Uppermost leaves sessile and lanceolate. Peduncle erect, glabrous (10–) 30–90 (−110) cm in length. Involucral bracts lanceolate to linear, patent. Inflorescence racemose and spicate, oblong to cylindrical, 30–80 mm in length, although the rachis continues to elongate from anthesis to fruiting. Flowers sessile, densely packed in bud but less so in flower, with 30–100 (−172) flowers in a single inflorescence. Single flowers also sometimes occur in the axils of the upper cauline leaves. Corolla 7–10 mm in length, sepals 5, petals 5, fused at the base and forming an upwardly curving tube in bud. Flowers hermaphrodite, stamens 5, filaments and anthers free, appressed around style. Style 1, stigmas 2–3, ovary 2–3 celled (usually 3), containing many (32–73) ovules. Seeds oval, reddish-brown, approximately 1.0 × 0.6 mm, with a mean air-dry seed mass ranging from 0.138 to 0.150 mg (based on 50–185 seeds per sample). Mean number of seeds per capsule in plants from Sussex (3.8–) 17.5 (−37.2) depending on inflorescence size and time of flowering (Wheeler 1997). Corresponding mean (± SD) values for material from Germany 46.7 ± 13.4 (Maier et al. 1999). The taxonomic status accorded to P. spicatum in continental Europe differs between authorities, and should still be considered provisional. Schulz (1904, in Kovanda 1981) recognized four subspecies (ssp. jurassicum R. Schulz, ssp. occidentale R. Schulz, ssp. coeruleum R. Schulz and ssp. ochroleucum Doll) to accommodate colour variants (in the first three) and morphological variation (in the fourth). Kovanda (1981) stated that in Czechoslovakia these subdivisions do not apply, and that the rare blue-flowered individuals are perhaps a hybrid of P. spicatum×P. nigrum. Damboldt (1976; Fl. Eur. 4) distinguished two subspecies –P. spicatum ssp. spicatum (corolla white to pale yellow with a greenish tip, stigmas yellow to yellowish-brown, found throughout the entire range of the species (Fl. Eur. 4)) and P. spicatum ssp. coeruleum R. Schulz (corolla blue, stigmas yellowish-brown to blue, confined to south-central Europe and the northern part of the Balkan peninsula (Fl. Eur. 4)). In all sites where the species occurs in East Sussex, UK, plants belong to ssp. spicatum. The white form of this subspecies is regarded as a native of Britain by many authorities (Hall 1980; Clapham et al. 1987). In contrast, garden escapes are usually blue-flowered (Stace 1997). In their account of the British flora, Bentham & Hooker (1954) placed a question mark after ‘native’ in their description of P. spicatum, and Grigson (1958) did not include the species at all. However, Hall (1980), Clapham et al. (1987), Stace (1997), Wheeler (1997) and Wheeler & Hutchings (1999) all regard P. spicatum as native. Phyteuma spicatum is known as a native plant in the British Isles only from East Sussex, vice-county 14 (Fig. 1). It was formerly more widely distributed within this vice-county than at present. It was recorded in a total of 24 different tetrads (2 km squares) and seven different 10-km squares in East Sussex between 1825 and 1996 (Wheeler & Hutchings 1999). It was also more abundant in recorded sites, particularly in the late 1800s and early 1900s (Wheeler & Hutchings 1999). By 1990, P. spicatum had become much reduced in its distribution within East Sussex and during 1996 it was recorded in only nine tetrads and four 10-km squares. Population sizes are also smaller now, with few sites supporting more than 10 plants (Wheeler & Hutchings 1999). The altitudinal range of the species in the British Isles is between 20 and 105 m a.s.l., although most sites are at c. 60–75 m a.s.l. The distribution of Phyteuma spicatum in the British Isles. Each dot represents at least one record in a 10-km square of the National Grid. Mapped by Henry Arnold, Biological Records Centre, Centre for Ecology and Hydrology, mainly from records collected by members of the Botanical Society of the British Isles. Native: (○) pre-1950; (•) 1950 onwards; introduced: (×) pre-1950; (+) 1950 onwards. Outside the British Isles, P. spicatum is endemic to Europe (mainly Central and Atlantic Europe) (Fl. Eur. 4). Its distribution extends from northern Norway and Estonia in the north to northern Spain in the south. It is found in Austria, Belgium, Bohemia, Bosnia, Britain, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Hungary, Italy, Luxembourg, the Netherlands, Norway, Poland, Romania, Serbia Slovenia, the Baltic, central and south-western regions of the former Soviet Union, Spain, Sweden and Switzerland (Atl. N. W. Eur.; Fl. Eur. 4). At the most northerly sites in which P. spicatum has been recorded, in northern Norway, it occurs in meadows, forest glades and disturbed ground associated in the past with German World War II camp sites. It is believed to have been imported with other exotic taxa in horse fodder between 1941 and 1944, since when its populations have persisted (Alm et al. 2000). Elsewhere it is most commonly found in woods and meadows. It is rare in lowland areas such as the Netherlands (Willems 1980; Weeda 1989), where it occurs in moist deciduous woodlands along streams on clay soils, and sometimes in grassy sites. Its range in the Netherlands has declined by between 25% and 50%, and it is now a Red Listed species (Van der Meijden 1990). It has also been described as common in the Meuse district and Lotharingen, and rare in the Ardennes, the western part of the Eiffel, Brabant and northern France (De Langhe et al. 1983). In Austria, Phyteuma spicatum grows in montane and subalpine woods at altitudes from 960 to 1500 m a.s.l. on 25–40° slopes (Ellenberg 1988). Oberdorfer reports an altitudinal range from 0 to 2110 m a.s.l. (Pfl. Exk.). Kovanda (1981) recorded that it is only locally frequent at lower altitudes in Czechoslovakia, but common in the mountains to the alpine belt. Hundt (1966, reported in Ellenberg 1988) recorded that P. spicatum occurred with increasing frequency in Trisetum flavescens meadows as altitude increased. In the British Isles, P. spicatum grows on the edges of paths and rides in woodland, on the sides of ditches and streams, and in hedge-banks on roadside verges. Plants are generally found in light shade cast by trees or scrub, but they are also rarely found growing in full sunlight on south-facing sites. The very limited distribution of P. spicatum in the British Isles precludes firm conclusions as to its climatic or topographical limitations in this country. However, plants cultivated from native seed thrive in the Botanic Gardens of the University of Cambridge, and blue-flowered garden escapes have been recorded in Warwickshire, Staffordshire, Merionethshire, Derbyshire and Roxburghshire (Perring & Farrell 1983), indicating that P. spicatum can grow in the colder climates of mid- and northern England, Wales and Scotland. Phyteuma spicatum was classed as a European temperate species by Preston & Hill (1997). It was considered suboceanic by Ellenberg (1988), growing mainly in the western parts of Central Europe which are influenced by westerly oceanic winds, but spreading towards the east. Oberdorfer describes it as a subatlantic to submediterranean species (Pfl. Exk.). Where it grows at higher altitudes in montane and subalpine pastures, average rainfall is much higher (1400–3000 mm year−1). Kovanda (1981) reports that P. spicatum is particularly abundant in leeward situations in mountain grasslands. In the British Isles, P. spicatum is found on the clays of the Ashdown Beds, and on the Weald Clay. These substrates range from being silty, with a subsurface horizon showing significant clay enrichment, to clayey soils or loamy soils overlying clay. Soils and subsoils are slowly permeable, and seasonal waterlogging is characteristic. Ellenberg Indicator Values for P. spicatum (Ellenberg 1988) in Central Europe define it as indifferent to soil reaction, and able to grow in soils with a wide range of pH. Ellenberg (1988) states that it is seldom found on especially nitrogen-rich or nitrogen-poor soils, although no values are given. He also stated that P. spicatum is absent from very wet or very dry soils. In Czechoslovakia, P. spicatum is regarded as indifferent to geological substratum, although it is favoured by deep, rich soils (Kovanda 1981). The sandy soils of stream valleys and the damp soils of brooks are favoured in the Netherlands (J. H. Willems, personal communication; Weeda 1989). Elsewhere in Europe, P. spicatum grows on moist soil in oak–hornbeam woodlands, slightly moist limestone soils in beech woods in the Swiss Jura, in depressions on heavy limestone brown loam and on deep rendzinas in the limestone Alps of Lower Austria, and on neutral loams over limestone to deep acid loams in beech and mixed beech woods (Ellenberg 1988). The communities in which Phyteuma spicatum is found in the British Isles are described below using the National Vegetation Classification system of Rodwell (1991, 1992). Phyteuma spicatum is found in Quercus robur–Pteridium aquilinum–Rubus fruticosus woodland (W10) communities, particularly the Anemone nemorosa subcommunity (W10b). The dominant species in the herb layer of this community are Anemone nemorosa, Hyacinthoides non-scripta, Lonicera periclymenum, Pteridium aquilinum and Rubus fruticosus agg., with the shrub and canopy layers dominated by Quercus robur, Carpinus betulus, Corylus avellana, Fraxinus excelsior, Pinus sylvestris (plantation) with some Tilia spp., Castanea sativa and Betula pendula. The Quercus–Pteridium–Rubus community is characteristic of base-poor brown soils with pH in the range 4.0–5.5, and is regarded as approximating the natural climax community for these soils (Rodwell 1991). Rodwell suggests that the vernal dominance of Anemone nemorosa is indicative of winter and spring waterlogging of the soil. On the edges of the paths and clearings some species generally found in low abundance and frequency in W10b woodland gain greater prominence. These species include Ajuga reptans, Circaea lutetiana, Oxalis acetosella, Potentilla sterilis, Rumex obtusifolius, Viola riviniana, and P. spicatum itself. The roadside verge communities are patchy. Plants of P. spicatum grow amongst tall scrubby vegetation typical of a Rubus fruticosus agg.–Pteridium aquilinum underscrub, Hyacinthoides non-scripta subcommunity (W25a). Pteridium aquilinum is often dominant in these communities, forming an almost continuous canopy by mid-summer, when P. spicatum is setting seed. Where P. spicatum grows in more open areas, often on the same roadside verges as those supporting the W25a community, the communities resemble mesotrophic grasslands. The grassland communities are variable, reflecting the variety of conditions available on the roadside verges where drainage ditches, weedy road verge margins and hedgebanks are common features. In these areas the communities are mostly similar to Arrhenatherum elatius grassland, Centaurea nigra subcommunity (MG1e) on more freely draining soils, with abundant Arrhenatherum elatius and Poa trivialis, and to Holcus lanatus–Deschampsia cespitosa grassland, Arrhenatherum elatius subcommunity (MG9b) on wetter soils. A number of species show a greater abundance than would typically be expected in these communities. These include some or all of the following: Dactylorhiza fuchsii, Lathyrus montanus, Listera ovata and Stachys officinalis on the drier parts of the verges, and Eupatorium cannabinum and Angelica sylvestris in the drainage ditches. Arrhenatherum elatius (MG1) and Holcus lanatus–Deschampsia cespitosa (MG9) communities are both considered the usual herbaceous antecedents of the Quercus–Pteridium-Rubus (W10) woodland community (Rodwell 1991). The Pteridium–Rubus (W25) community shows a strong resemblance to the vegetation of the Quercus–Pteridium–Rubus (W10) woodland community, and is generally found in association with woodland, or as a relict of woodland that has been felled or grubbed out (Rodwell 1991). This is certainly the case at the site of the largest population of P. spicatum in the British Isles, where the roadside verge borders a block of land which was wooded until the 1960s, when the trees were felled and the land converted to pasture. A phytocentric vegetation survey was carried out at the site of the largest P. spicatum population still extant in the British Isles. The site lies on the clay of the Ashdown beds at an altitude of 60 m a.s.l. The soil is a silty stagnogleyic argillic brown earth, with a subsurface horizon with significant clay enrichment causing seasonal waterlogging, and a slowly permeable subsoil. Soil pH at this site ranged from 3.7 to 4.4 (n = 10). Percentage frequency of aerial parts, mean cover recorded on a Domin scale (after Dahl & Hadač 1941), and percentage rooted frequency, were estimated for all species. The frequency and cover of bare soil and litter were also recorded. The general community at the site was recorded in randomly located circular quadrats of diameter 9 cm, and the vegetation immediately surrounding plants of P. spicatum was recorded in circular quadrats of the same size, centred on randomly selected P. spicatum plants. The abundance and frequency of species were then compared for sites in which P. spicatum was and was not present (Fig. 2a,b). Analyses of the composition of vegetation in 9-cm diameter circular plots centred on randomly selected P. spicatum plants, and the composition of the vegetation in 9-cm diameter circular plots located at random in the same site. (a) Percentage frequency of aerial parts of species. (b) Mean Domin scores (Dahl & Hadač 1941) based on aerial parts of each species. (c) Percentage rooted frequency of each recorded species. Data points lying on the diagonal lines indicate that recorded values for species were equal in the quadrats centred on P. spicatum and in quadrats located at random. Species with which P. spicatum shows an affinity are above the diagonal. Species with which P. spicatum shows a negative association are below the diagonal. Only species for which P. spicatum showed a marked affinity or negative association are labelled with a species code. The identity of species labelled with a code is as follows: Ae − Arrhenatherum elatius, Dg − Dactylis glomerata, Ga − Galium aparine, Hn − Hyacinthoides non-scripta, Pa − Pteridium aquilinum, Ps − Potentilla sterilis, Pt − Poa trivialis, Rf − Rubus fruticosus agg., Ts − Teucrium scorodonia, Vc − Veronica chamaedrys, Vr − Viola riviniana. Key for Domin scale: 1, < 4% (few individuals); 2, < 4% (several individuals); 3, < 4% (many individuals); 4, 4–10%; 5, 11−25%; 6, 26–33%. The percentage frequency and cover of bare ground and litter were both considerably higher in samples centred on plants of P. spicatum than in samples sited at random (Fig. 2a,b). Of the two most frequently recorded grasses in the community (Fig. 2a), Poa trivialis was more frequently recorded (and rooted) in samples centred on P. spicatum than in the general community, whilst the reverse was true for Arrhenatherum elatius (Fig. 2a,c). Few other species were present in more than 20% of the samples (Fig. 2a). Of those that were, Dactylis glomerata, Rubus fruticosus agg., Viola riviniana and Potentilla sterilis were more frequently recorded in samples centred on P. spicatum, whereas Pteridium aquilinum and Galium aparine were more frequently recorded in samples located where P. spicatum was absent. Hyacinthoides non-scripta, Teucrium scorodonia and Veronica chamaedrys displayed similar frequencies and cover in samples where P. spicatum was absent and in samples where it was present. Percentage similarity (Pielou 1975, p. 100) was calculated on percentage frequency of aerial parts, mean cover (Domin scale) and percentage rooted frequency (Fig. 2c) for all species recorded in the samples taken at random and in the vegetation immediately surrounding P. spicatum plants. Percentage similarity values were 74.7%, 67.6% and 64.8% for frequency of aerial parts, mean cover and rooted frequency, respectively. In summary, there were differences in composition at the study site between vegetation samples collected from the vicinity of P. spicatum plants and from locations from which it was absent, although the species composition in both sets of samples was similar. The lowest similarity value was for percentage rooted frequency of species. Phyteuma spicatum showed an affinity for sites where bare ground and litter were abundant, and for sites where aerial parts of Rubus fruticosus agg. and rooted Poa trivialis were frequent (Fig. 2a,b), whereas it was usually absent from sites where aerial parts of Pteridium aquilinum and rooted Arrhenatherum elatius were frequent (Fig. 2a,b). Presumably, the dense canopy and the highly competitive nature of the last two species impeded establishment and growth of P. spicatum. Ellenberg (1988) names P. spicatum as a component of the herbaceous community in several tabulated summaries of communities from Central Europe. It is a ‘character species’ (Pfl. Exk.; Ellenberg 1988) of the ‘noble broadleaved woods’ (Fagetalia) where, on rich to average nutrient status brown-mull soils, it is associated with Anemone nemorosa, Athyrium filix-femina, Brachypodium sylvaticum, Carex sylvatica, Dryopteris filix-mas, Galium odoratum, Hedera helix, Lamiastrum galeobdolon, Luzula pilosa, Lysimachia nemorum, Milium effusum, Polygonatum multiflorum and Viola reichenbachiana (Ellenberg 1988). Phyteuma spicatum is also widely distributed in Central Europe in lime– and oak–hornbeam woods, and it occurs in silver birch–fir woods, and also in the herbaceous margins of woodland, woodland edges, scrub and hedges with, for example, Agrimonia eupatoria, Fragaria vesca, Hypericum perforatum, Plantago lanceolata, Ranunculus ficaria, Scabiosa columbaria, Stachys officinalis and Stellaria holostea (Ellenberg 1988). In montane and subalpine Trisetum flavescens meadows, P. spicatum is associated with Astrantia major, Campanula scheuchzeri, Geranium sylvaticum, Muscari botryoides, Phyteuma halleri, Poa chaixii, Primula elatior, Rumex arifolius and Silene dioica (Ellenberg 1988), whilst in the Massif Central, France, and in the Pyrenees, common associates are Astragalus purpureus, Campanula glomerata, C. persicifolia, Convolvulus cantabrica, Erinus alpinus, Saponaria ocymoides and Vicia onobrychioides (Polunin & Smythies 1973). Oberdorfer describes P. spicatum as a species of broad-leaved and mixed broad-leaved–coniferous woodland with a rich understorey, and as a characteristic species of the Orders Polygono-Trisetion and Adenostylon in mountain grasslands on moist, lime-rich and lime-poor nutrient-rich basidophylic soils (Pfl. Exk.). Although Ellenberg (1988) stated that P. spicatum exhibits ‘indifferent behaviour to light, i.e. a wide amplitude’, there is some evidence from sites in the British Isles that it ceases to flower in deep shade, and that it ultimately fails to survive in prolonged deep shade. A number of sites for which there were records of P. spicatum flowering in 1986 (FitzGerald 1988) were found, during surveys in 1996, to contain only vegetative plants. These sites had become shaded by the growth of surrounding herbaceous vegetation or by the closure of the canopy. In one woodland site containing several areas recorded historically as containing P. spicatum, a search in 1986 recorded flowering plants only in a recent tree-fall area (FitzGerald 1988). By 1996, part of this tree-fall area had become overgrown with Rubus fruticosus agg., and no plants of P. spicatum could be located. A study of establishment and survival of seedlings of P. spicatum in cleared and uncleared plots at the site of the largest British population was carried out from December 1994 to July 1996 (Wheeler 1997). Prior to clearance, the plots were densely vegetated, with Pteridium aquilinum dominant. Only above-ground biomass was removed. Percentage germination was significantly higher in cleared plots than in uncleared plots (9.0 ± 2.3% vs. 1.4 ± 0.6%, P < 0.05). At the termination of the experiment, 84 weeks after the seeds were sown, 31.7% of the seedlings which had germinated in the cleared plots remained alive (equivalent to 2.9% of the total number of seeds sown). No seedlings survived in the uncleared plots (Wheeler 1997). Plants of P. spicatum tend to have a clumped distribution. Most dispersed seeds land close to parent plants and therefore new recruits to populations are positioned close to established plants. During investigations of a population of P. spicatum during 1994, the mean (± SE) distance recorded from plants of P. spicatum to their closest neighbour was 0.27 ± 0.03 m, with 53.4% of nearest neighbours less than 0.20 m apart (Wheeler 1997). Single plants can produce numerous rosettes arising from different positions on the rootstock. In such cases, rosettes emerging from the same rootstock are rarely more than 5 cm apart. Weeda (1989) observed that in the Netherlands P. spicatum was less well adapted to human interference than the closely related species P. nigrum. In the Drenthe locality, P. spicatum has gradually been replaced by P. nigrum where areas of old woodland have been converted to grassland. In the British Isles, P. spicatum has disappeared from most of its historic sites (Wheeler & Hutchings 1999) in traditionally managed woodland and on roadside verges. Both of these habitat types were formerly subject to human interference, through coppicing and timber extraction in the first case, and hay cutting in the second. It is likely that in the British Isles it is not human interference that the species cannot tolerate, but neglect in the case of formerly managed woodlands, or, in the case of roadside verges, the change to intensive management practices that may not meet its habitat requirements because methodology or timing is inappropriate for its survival (Wheeler 1997). Severe drought caused wilting in plants grown in a glasshouse and in container-grown plants of P. spicatum that were kept outdoors. Prolonged periods at temperatures higher than 25 °C in glasshouses caused the above-ground parts of plants to die, but the majority of these plants maintained a living root system which produced above-ground parts in the following year. Frost damage has not been recorded in container-grown plants. Phyteuma spicatum initiates leaf production during winter. As its distribution range includes subalpine and montane meadows, it is unlikely to suffer damage from mild frost. Waterlogging of glasshouse-grown plants caused the primary root to rot. Several weeks of impeded drainage resulted in the death of plants (B. R. Wheeler, personal observation). The primary root of P. spicatum becomes thickened and fleshy while the plant is still at the seedling stage. The root can be napiform or fusiform in shape, but it is often irregular and variable. Ellenberg (1988) reported that the root changes in form in response to the acidity of the top soil. Very acid soils (pH 4–5) promote the growth of shallow, horizontally orientated roots in the top few centimetres of soil where the nutrient content is higher and the soil is less acid. In less acidic soils (pH > 6) roots grow more vertically and penetrate deeper. The annual rosettes of leaves are produced from slightly different parts of the rootstock each year, although they are generally formed near the rootstock apex. Rosettes from previous years leave a scar. Rootstocks can bear numerous rosettes, and the number of rosettes tends to increase with rootstock age. Salisbury (1928) recorded from 0 to 4 stomata mm−2 on the upper (adaxial) surface of leaves of P. spicatum, and 146–218 stomata mm−2 on the lower surface, with a mean of 176 stomata mm−2. The material used was from plants collected from British woodlands, and P. spicatum was included as a component of the herbaceous ‘shade flora’ in a tabulated summary. The stomatal density on the upper and lower surfaces of leaves of P. spicatum was similar to that of the other species included in this group, in which stomata were either absent (in 75.6% of species examined) or low in density (a range of 0–99 stomata mm−2) on the upper surfaces, and present on the under surface (in 100% of species examined) at a higher density (a range of 10–316 stomata mm−2). Salisbury also calculated a stomatal index for density of stomata in relation to number of epidermal cells, using the equation (S/(E + S)) × 100, where S is the number of stomata per unit area and E is the number of epidermal cells in the same area. The stomatal index for P. spicatum ranged from 17.9 to 25.0, with a mean value of 21.1. This value was in the centre of the range of mean stomatal index values calculated for a total of 14 woodland species (Salisbury 1928). Harley & Harley (1986) cite four studies which have reported vesicular-arbuscular mycorrhiza (VAM) in P. spicatum, one study in which mycorrhizas were recorded as absent and another in which some specimens had no fungal colonization and others displayed VAM colonization. Phyteuma spicatum is a herbaceous perennial which produces annual rosettes of basal leaves from the axils of cataphyllary leaves (Kovanda 1981), and one to many inflorescences on upright stems. Leaves and inflorescences die back in the winter. Reproduction is thought to be entirely by seed, which is shed in August, and germinates during late winter or early spring of the following year. Thompson et al. (1997) record P. spicatum as having a transient seed bank (based on Von Borstel 1974), but Wheeler (1997) obtained evidence that some seeds can survive in the soil for more than one year, and that seeds can cycle through periods when germination is possible and periods when it is prevented by dormancy mechanisms. Huber (1988) investigated spontaneous autogamy and geitonogamy in continental plants of P. spicatum. She bagged whole inflorescences prior to anthesis, and recorded their seed production. The majority of flowers produced no seed, but a small number (on average 1–2 per plant) produced 1 or 2 seeds. Similar experiments were carried out by Kovanda (1981), with the result that 0–3 seeds were produced per flower capsule. Huber (1988) also estimated the percentage of ovules that ripened per plant following hand-pollination of flowers using pollen from flowers on the same inflorescence (i.e. geitonogamous pollination). The flowers treated in this way were then bagged until the capsules had ripened. From 0.17% to 1.18% of ovules per plant produced ripe seed following geitonogamy, resulting in the production of a mean of 0.07–0.36 seeds per capsule, compared with a recorded mean production of 31.2 ± 4.3 seeds per capsule by medium-sized inflorescences during peak seed set in a British population of P. spicatum (Wheeler 1997). Huber (1988) observed reduced growth of pollen tubes inside the style on flowers pollinated geitonogamously compared with those pollinated by allogamy, and concluded that gametophytic incompatibility may be responsible for the low levels of seed production observed after self-pollination. Autogamy or geitonogamy may therefore be possible under natural conditions but likely to result in very low seed production. It is probably of low importance in seed production in populations where cross-fertilization can occur. Cross-fertilization can result in the production of up to 50 seeds per capsule in plants with close neighbours (Wheeler 1997). Relatively isolated plants of P. spicatum (at least 90 m from larger concentrations of plants) produced no seed (B. R. Wheeler, personal observation). The mean number of seeds produced per seed capsule in Sussex was examined in 1995 in inflorescences from each of three size classes (< 25 mm, 25–50 mm and > 50 mm inflorescence length). For each of five inflorescences in each size class, the ripe seed number was recorded from each of two undehisced seed capsules taken from near the base and near the top of the inflorescence. Inflorescences in each size class that flowered early and set seed during the main period of seed set, in July, and inflorescences that flowered late, and set seed late, in August, were examined. The mean number of seeds per capsule ranged from 3.8 to 37.2, with a mean of 17.5 for all samples. The mean number of seeds produced per capsule was significantly greater for all size categories for inflorescences that developed early (Wilcoxon non-parametric test for matched pairs, P < 0.05 for all size classes). In inflorescences that developed late there was little variation between size classes in mean seed production per capsule (mean ± SE ranged from 6.6 ± 1.0 in medium-sized inflorescences to 10.5 ± 3.1 seeds in small inflorescences), whereas seed production was significantly higher in large and medium-sized inflorescences than in small inflorescences that flowered at the peak of the flowering