Andromeda polifoliaL.

Abstract

A low, glabrous, evergreen shrub, (5)–10–25–(40) cm tall. The flowering stems are decumbent to erect, sparingly branched, arising from a creeping, woody rhizome (Warming 1908; Fl. Eur. 3; Fl. Br. Isl.; Hegi Fl. 1, ed. 3; Rameau et al. 1993; Stace 1997). The leaves are narrow, alternate, subsessile, coriaceous, oblong to linear, dark green above, silvery-glaucous beneath, 10–40 × 2–8 mm (Barvaux 1958; Fl. Eur. 3; Fl. Br. Isl.; Rameau et al. (1993); Stace 1997). They are mucronulate (Anderson 1961) or acute to apiculate (Fl. Eur. 3); their margins are usually revolute (Fl. Br. Isl.; Rameau et al. 1993). The flowers are pentamerous (Barvaux 1958; Anderson 1961; Hegi Fl. 1, ed. 3), in very short, umbel-like terminal racemes of 2–7–(12) (Warming 1908; Fl. Eur. 3; Rameau et al. 1993). However, Warming (1908) reported 4-merous flowers in Finnmark and in Greenland. The pedicels are pinkish, 2–4 times as long as the corolla (Barvaux 1958; Fl. Br. Isl.; Hegi Fl. 1, ed. 3); they are 7–15 mm long and slender (Fl. Eur. 3). The sepals are persistent, triangular, reddish, acute, about 1.5 mm long (Anderson 1961; Fl. Eur. 3) and connate at base (Fl. Eur. 3). Two bracteoles lie at the extreme base of the pedicel, concealed by a bract (Fl. Eur. 3). Corolla globose-urceolate with 5 recurved teeth; drooping (Webb 1967), inclined or pendent (Fl. Eur. 3), bright pink at first, fading almost to white. It reaches 5–8 mm long (Warming 1908; Barvaux 1958; Anderson 1961; Fl. Br. Isl.; Hegi Fl. 1, ed. 3; Rameau et al. 1993) and it continues to grow during flowering (Warming 1908). The interior of the corolla is covered with erect, usually somewhat upturned, hairs that extend to the margin of the limb (Warming 1908). The stigma lies just at or immediately within the throat of the corolla, and the 10 anthers, which are at the level of the middle of the pistil and the corolla, bend inwards towards the style (Warming 1908; Barvaux 1958; Hegi Fl. 1, ed. 3; Rameau et al. 1993). The filaments are strongly swollen just above their slender short bases and are covered with fairly long hairs along the greater part of their length (Warming 1908; Anderson 1961). The anthers are covered with small protuberances; they open at the apex by two pores of irregular shape (Warming 1908; Hegi Fl. 1, ed. 3). The two apical appendages are as long as the anthers, glabrous and slightly curved (Warming 1908; Anderson 1961; Fl. Eur. 3). Pollen tetrad diameter ranges between 36 μm and 60 μm (Oldfield 1959; Paquereau 1959; Visset 1971; Hebda 1979; Warner & Chinnappa 1986). The mean number of tetrads per anther reaches 317 (range 277–428; Hebda 1979) or 403 (range 325–468; A.-L. Jacquemart, unpublished data). The stigma is not always distinctly lobed, but sometimes there are five small, rounded projections upon it covered by a thick mucilage that it secretes (Warming 1908). The nectar is secreted by swellings at the base of the ovary (Warming 1908; Fl. Br. Isl.). The superior ovary is 5-celled, with a mean of 46.0 ovules in Belgium (± 1.1, n = 10; A.-L. Jacquemart, unpublished data) or 47.2 in Sweden (Fröborg 1996). Baranec et al. (1996) counted a mean of 40 oval-shaped ovules, with 8 ovules per carpel. The fruit is an erect, loculicidal (Fl. Eur. 3), subglobose, 5-valved and glaucous capsule (Anderson 1961; Hegi Fl. 1, ed. 3). The capsule is 2.2–4.5 mm wide and 1.4–4.7 mm in height (Fl. Eur. 3). Seed number per capsule ranges between 1 and 44 (A.-L. Jacquemart, unpublished data). The seeds are oval, smooth (Fl. Br. Isl.), bright, elliptic, brown (Rameau et al. 1993), 0.4–0.8 × 0.7–1.5 mm (Hegi Fl. 1, ed. 3). In Belgium, the fresh mass of 100 seeds averages 21.97 ± 0.49 mg (n = 20) (A.-L. Jacquemart, unpublished data). Native, mainly on Sphagnum-rich ombrogenous bogs and rarely on other wet, acid habitats, mostly lowland (Webb 1967; Fl. Eur. 3; Fl. Br. Isl.). The distribution of A. polifolia in the British Isles is shown in Fig. 1. This species is in decrease (Stewart et al. 1994). It is now virtually absent from southern and much of central England as well as some parts of Scotland. It is extinct in Somerset, Norfolk and Hunts (Fl. Br. Isl.) but it has been re-introduced into Somerset (transplants from Cumbria). In Ireland, it occurs in the Central Plain, and extends to Antrim, East and West Mayo, Limerick and Wicklow (Fl. Br. Isl.; Webb (1967); Foss et al. 1984). Thus it has been reduced drastically in England and in Ireland, as shown in Fig. 1, where a considerable number of records are pre-1950 only (Birse 1980; Foss et al. 1984; Stewart et al. 1994; Stace 1997). The undisturbed raised mire habitat has suffered severely from drainage, afforestation, heather burning and peat digging in recent years, and A. polifolia has correspondingly become more local (Stewart et al. 1994). Often the extinction in West Europe results almost certainly as a consequence of drainage of bogs, particularly in association with peat extraction (Mennema et al. 1985; Rodwell 1991; B.D. Wheeler, personal communication). The distribution of Andromeda polifolia in the British Isles. Each dot represents at least one record in a 10-km square of the National Grid. (○) Pre-1950; (•) 1950 onwards. Mapped by the Biological Records Centre, Institute of Terrestrial Ecology, using Dr A. Morton's DMAP program, mainly from data collected by members of the Botanical Society of the British Isles. The species is present in all circumboreal regions (Anderson 1961; Hegi Fl. 1, ed. 3; Oberdorfer 1983; Hultén & Fries 1986; Billings 1988). It occurs in North and Central Europe from Scandinavia (not Iceland) to Normandy, the Auvergne, South Alps, northern Spain, northern Italy, North and South Germany, Central Switzerland (low places), East Carpathians and Central Russia (Fig. 2), mainly in the mountains in the southern part of its range (Fl. Br. Isl.; Hegi Fl. 1, ed. 3; Hultén 1971; Fitter 1978; Welter & Ruben Sutter 1982; Hultén & Fries 1986; Haeupler & Schönfelder 1989). According to Hegi (Fl. 1, ed. 3), it has disappeared from Spain, Croatia and Romania. It is considered as a rare species and it is protected in France (occurs only in the Vosges, Jura, Savoie, Massif Central, Pyrénées & Normandie; Rameau et al. 1993) and in the Netherlands (Mennema et al. 1985). It is also found in North Asia to Japan; Greenland; North America south to New York and Idaho (Fl. Br. Isl.; Fl. Eur. 3; Hultén & Fries 1986). The northern limit seems to lie a long way north of the Arctic Circle to about 71°7′ or even 74° (Hegi Fl. 1, ed. 3; Hultén & Fries 1986). The European distribution of Andromeda polifolia based on information in the literature. (£) Common; (!) less common. In the British Isles, A. polifolia occurs from sea level up to about 530 m in England and Wales (Ward's Stone and Bottom Head Fell), 735 m on Mount Keen and about 460 m in Ireland (Alt. range Br. Pl.; Stewart et al. 1994). In continental Europe, it may be found up to 1700–2000 m (Hegi Fl. 1, ed. 3; Rameau et al. 1993). This species is considered as boreo-alpine (Barvaux 1958), circumboreal (Rameau et al. 1993) and circumpolar boreal-montane (Preston & Hill 1997). It is circumpolar in northern areas, although its range extends to Central Europe and it is absent from the oceanic Atlantic coast; it occurs chiefly in the arctic and taiga biomes (Lindholm 1982; Hultén & Fries 1986). In Britain, Rodwell (1991) gives A. polifolia at mostly low altitude, between 10 and 530 m. These areas have between 800 and 1200 mm annual precipitation, with around 140–180 wet days year−1 (Rodwell 1991; Schaminée et al. 1995). It occurs at greatest shoot frequency in low hummocks and lawns of ombrotrophic bogs (Lindholm & Vasander 1981). It is successful at the alpine-montane level in oceanic and suboceanic regions of mainland Europe (Rameau et al. 1993). Andromeda polifolia is found on acid soil types. The humus type is peat, dysmoder or mor; all the soils are poor in bases and in nutrients (Small 1972; Rameau et al. 1993). It occurs on virgin surfaces where there is consistent waterlogging, with a high water-table, which favours the luxuriant growth of peat-building Sphagna (Small 1972; Rameau et al. 1993). These sites are uniformly acidic at the surface, with a pH between 3.8 and 4.3 in UK and West Europe (Rodwell 1991; Schaminée et al. 1995) or 4.6–5.0 in Scandinavia (Malmer & Nihlgaård 1980; Heikkilä 1987). Andromeda polifolia is not especially a hygrophilous species; it can grow well in quite dry soils and can persist in drained bog vegetation long after Sphagnum species have disappeared. Apart from the fact that drainage is usually associated with some other, more detrimental, activity (e.g. peat removal, afforestation), thus greatly augmenting its impact, when drying is detrimental to Andromeda this has probably more to do with species interactions than any direct influence of low water levels (B. D. Wheeler, personal communication). It grows thus on elevated Sphagnum hummocks. Where the drier vegetation has little Sphagnum (when it is strongly dominated by Calluna), A. polifolia is often scarce or absent, although when it does occur individual plants are often considerably more robust than in the case of Sphagnum lawns. The habitat of A. polifolia in Britain and Ireland is best described as oligotrophic with low pH (3.1–5.0), few exchangeable cations and little available nitrogen and phosphorus (Small 1972; Malmer & Nihlgaård 1980; Malmer & Wallén 1986; Heikkilä 1987; Cullings 1996). This species is considered as hygrophilous–acidophilous by Rameau et al. (1993). The chief habitat of the plant is the main dome of raised bogs over much of North West Europe. It extends into wet hollow communities, wooded bogs and occasionally blanket bogs. The following treatment of its phytosociological behaviour in Britain is based on the National Vegetation Classification (Rodwell 1991). Andromeda polifolia occurs typically in the Erica tetralix–Sphagnum papillosum mire (M18). This mire community is generally dominated by Sphagna, with ericoid subshrubs and monocotyledons often playing a more or less important role, Calluna vulgaris, Erica tetralix and Eriophorum vaginatum being the most common species. Andromeda polifolia and Vaccinium oxycoccos are distinctive of the Sphagnum magellanicum–Andromeda polifolia subcommunity (M18a); these two continental northern species have their British distributions largely centred in the regions where this community is found. This community is characteristic of waterlogged ombrogenous peats, typically at low altitudes in the moderately oceanic parts of Britain (lowlands of Wales, north-west England and Scotland, with less frequent occurrence in blanket bog at higher altitudes (> 300 m) and with a few outlying sites in lowland eastern England). Greatest frequencies of A. polifolia are usually associated with a Sphagnum-rich carpet, and one that usually contains a variety of Sphagnum species, often including Sphagnum magellanicum (Tüxen 1980; Doyle & Moore 1980; Rodwell 1991). Andromeda polifolia also occurs in the Sphagnum cuspidatum/recurvum bog pool community (M2), especially in the Rhynchospora alba–Sphagnum cuspidatum subcommunity (M2a) but not in the wettest locations. Andromeda polifolia can sometimes also be found in the Sphagnum recurvum subcommunity (M2b), with Erica tetralix, Eriophorum angustifolium, Vaccinium oxycoccos and Drosera rotundifolia. Nevertheless, Rhynchospora is absent and Andromeda is much less abundant in this second subcommunity. The community is dominated by extensive soft wet carpets of Sphagnum recurvum; vascular plants typically occur as scattered individuals of low total cover. This community is found in pools and hollows on very wet and base-poor ombrogenous mires in the less oceanic parts of Britain (Wales, the Borders, south-west Scotland and some localities in north-east Scotland). Andromeda polifolia does extend into these Rhynchosporion communities but becomes increasingly sparse with increased wetness. In Ireland, the species is fairly common in ombrotrophic peatland but is of restricted distribution in Atlantic blanket bog (Doyle & Moore 1980; Doyle 1990; Schouten 1990). Braun-Blanquet & Tüxen (1950) reported the species only in the subassociation with A. polifolia of the Pleurozia purpurea–Erica tetralix (Lid 1929) Br.-Bl. & Tx 1950 association (in the Oxycocco-Sphagnetea class). It is also worth noting that in Britain and parts of mainland Europe (as opposed to Fennoscandia), A. polifolia is almost exclusively a plant of ombrogenous peatlands. In Britain, it is more closely confined to these than any other vascular plant. There are a few sites in which it also grows in weakly minerotrophic conditions, but these are usually alongside ditches cut into an ombrotrophic surface, or instances where a once Sphagnum-rich ombrotrophic surface has been subject to recent, mild enrichment (B. D. Wheeler, personal communication). Outside Britain, A. polifolia is characteristic of Sphagneta with Vaccinium oxycoccos, Carex spp. and Vaccinium uliginosum, as well as Drosera rotundifolia, Ledum palustre, Betula nana and Calluna vulgaris (Hegi Fl. 1, ed. 3). In Fennoscandia, the species is rather common in poor fens and in transitional rich fens (Eurola 1962; Dierssen & Dierssen 1980). For example, in Finland, this oligotrophic species occurs in meso-eutrophic mud-bottom flark fens and Calliergon stramineum flark fens. It also appears at lower frequency in mesotrophic mud-bottom flark fens, eutrophic Sphagnum obtusum fens, meso-eutrophic Molinia fens and eutrophic pine and spruce swamps (Heikkilä 1987). In Swedish mires, A. polifolia occurs on hummock-lawns (Kvillner & Sonesson 1980) with Eriophorum vaginatum, Empetrum hermaphroditum and principally mosses such as Sphagnum balticum. It is present in the Empetrum hermaphroditum–Vaccinium microcarpum (= Empetro-Sphagnetum fusci Du Rietz 21 emend. Dierssen 82) association, mainly in three variants: the Cetraria nivalis–Dicranum elongatum variant (100% frequency), the Dicranum elongatum–Sphagnum balticum variant (92% frequency) and the Eriophorum vaginatum–Sphagnum russowii variant (100% frequency) (Sonesson & Kvillner 1980). It also occurs in the Carex rotundata–Drepanocladus schulzei association (in all variants with a frequency of 17–86%) (Sonesson & Kvillner 1980). In general, in western Europe, A. polifolia occurs in two phytosociological classes: the Oxycocco-Sphagnetea Br.-Bl. & Tx. 43 and the Scheuchzerietea DenHeld, Barkman & Westhoff 69 (Oberdorfer 1957, 1983; Tüxen 1980; Dierssen 1980; Schaminée et al. 1995). It occurs principally in the Oxycocco-Sphagnetea, which is typical of ombrogenous raised peat bogs. The species occurs in the Sphagnetalia-magellanici (Pawlowski 28) Kästn. & Flösn. 33, in the Oxycocco-Ericion (Nordh. 36) Tx. 37 in two associations: the Erico-Sphagnetum magellanici Osvald 23 and the Sphagno palustris-Ericetum Meltzer 45. It is also found in the Erico-Sphagnetalia Schwick. 40 emend. Br.-Bl. 49, in wet heaths (= Ericion tetralicis Schwick. 1933) in one association, the Ericetum tetralicis Allorge 22 (Oberdorfer 1957, 1983; Lecointe & Provost 1977; Schaminée et al. 1995). In the second class – represented in bog pools and poor fens, including floating mats – it is present in two alliances, the Rhynchosporion albae Koch 26 within three associations (the Sphagnetum cuspidato-obesi Tx. & vs. Hübschm. 58, the Sphagno-Rhynchosporetum Osvald 23 and the Caricetum limosae Osvald 23), and the Caricion lasiocarpae Vanden Berghen 49 in the Eriophoro-Caricetum lasiocarpae Osvald 23 (Oberdorfer 1957, 1983; Schaminée et al. 1995). In Germany as well as in the Netherlands, Oberdorfer (1957, 1983) noted its occurrence in the Pino-Ledion Tx. 55 and in the Piceon-Pinion uncinatea Tx. 55. The annual height increment of the moss layer is usually in the range 1–5 cm year−1 on hummocks and more than 10 cm year−1 in pools or wet depressions (Lindholm 1982; Malmer et al. 1994), and most of the dry matter in A. polifolia is beneath the moss layer (Lindholm 1982). Such growth rates often equal the annual shoot growth rate of the dwarf shrub species co-occurring with the Sphagnum mosses (Malmer et al. 1994). Owing to the continuous upward growth of Sphagnum, the vascular plants growing in bogs need to put resources into vertical growth to keep pace with the Sphagnum carpet (Malmer et al. 1994; Svensson 1995). A minimal yearly average increment in Sphagnum fuscum of 2 mm (Sonesson 1972 cited by Wallén 1986: probably a minimum value on the Swedish site studied) implies a yearly embedding of at least 4 g m−2 of wood of A. polifolia (Wallén 1986). For a steady-state above-ground biomass, this implies a minimum annual embedding of about 20% of the wood above the moss surface (Wallén 1986). The influence of the vascular plants on the growth and development of Sphagnum is considered to be of less importance than the reverse (Malmer et al. 1994). Both the vascular plants and Sphagnum mosses must be regarded as highly stress-tolerant, with a highly conservative strategy with respect to the acquisition and use of mineral nutrients (Malmer & Wallén 1986; Stewart & Nilsen 1995). As the two groups of plants are dependent on different sources for this resource, it cannot be shown that they compete directly for it (Malmer et al. 1994). On the other hand, the presence of Sphagnum obviously reduces the supply of mineral nutrients to the vascular plants and, in that sense, Sphagnum competes with the other plants by capturing a limiting resource before the vascular plants can do so (Malmer et al. 1994). Andromeda polifolia can recolonize peat workings on ombrogenous bogs: it rapidly establishes on drier soil but is often only a late recolonist of wetter, revegetating workings (Smart et al. 1989). There were 1220 ± 209 live tillers m−2 (n = 42 quadrats) in a Swedish mire, with a mean of 1.21 ± 0.06 shoots per individual tiller (Flower-Ellis 1980). The tillers are sparsely branched and each has approximately eight (7.83) leaves distributed between four leaf generations (Flower-Ellis 1980). There were 3.71 ± 0.28 current-year leaves per shoot, 1.22 ± 0.04 1-year leaves, 0.73 ± 0.08 2-year leaves and only 0.12 3-year leaves (Flower-Ellis 1980). The mean number of flowers or capsules is very variable; not all tillers flower and flowering individuals have several flowers, exceptionally 20–30. Abundant flowering is associated with reduced current shoot production, consequently with reduced total leaf number and area (Flower-Ellis 1980). Tillers with numerous flowers therefore have both a smaller assimilating area, relatively older leaves and a larger sink for assimilate above-ground, than purely vegetative tillers of equivalent age and size (Flower-Ellis 1980). The rhizome must be assumed to be common to both flowering and non-flowering tillers (Flower-Ellis 1980). The leaves remain green on the stems throughout at least one winter (Warming 1908) and 4 years at the most (Flower-Ellis 1973, 1980). Not more than about 5% of the current-year leaves appear to die in the interval between their appearance and that of the next year's leaves (Flower-Ellis 1980). By the end of their second growing season, a mean of 59% of those initially present have fallen. By the end of the third season, 62% of the original number have fallen. By the end of the fourth season, 96% have fallen. Some older leaves (more than 3 years) may persist until the end of the fourth growing season on the elevated areas in northern Sweden, but are exceedingly uncommon (Flower-Ellis 1980). The leaves of plants growing in hummocks are larger (72.9 cm2 vs. 59.4 cm2) and heavier (14.7 mg vs. 10.0 mg fresh mass) than those from the hollows (Simonis & Hirsch 1962). Flower-Ellis (1980) showed the same trend: leaves from hummocks are longer (7–13 mm vs. 7–11.5 mm) and the capsules are heavier (5–16 mg vs. 5–13 mg) than those of plants in hollows. Moreover, current-year leaves contain about 0.51% fresh weight nitrogen in hollows and 0.65% in hummocks (Simonis & Hirsch 1962). The same higher proportion for plants in hummocks was also detected for 1-year leaves (0.49% and 0.58% fresh weight N, respectively) (Simonis & Hirsch 1962). The mean dry weight of the aerial biomass is about 10 g m−2 in southern Finland (Lindholm & Vasander 1981) and about 28 g m−2 (Flower-Ellis 1973, 1980) or averaging 17 ± 2 g m−2 (Wallén 1986) in northern Sweden. Both the number of branches and the number of flowers vary with age and with microsite (Flower-Ellis 1980). The intermediate slopes of the elevated areas, and hummocks in small depressions, have both the most abundantly branched tillers and the largest numbers of flowers (Flower-Ellis 1980; A.-L. Jacquemart, unpublished data). Andromeda polifolia suffers more from frost on more open communities (Lindholm & Vasander 1981). Plants on the high hummock community withstand frost damage better than those of open communities (Lindholm & Vasander 1981). There is also a clear difference between the morphology of the tillers of the individuals of the high hummock community and of the other more open habitats. The tillers of the former habitat were upright and long compared with the tillers of the other habitats, which were stunted and low (Lindholm & Vasander 1981; Lindholm 1982). Fröborg (1996) estimated the fruit set in central Sweden to be about 65%. Flower-Ellis (1980) considered that most of the flowers in a northern Swedish mire develop into capsules, although not all capsules ripen. The limit of the potential resistance of ericaceous dwarf shrubs to low temperatures during the growing season is generally about –5 °C (Lindholm 1982). Many arctic and boreal plants are tolerant of low temperatures during the dormant phase, but during the active phase they are sensitive even to brief periods of low temperatures (Lindholm 1982). Frost caused considerable loss of production in destroying current shoot tips and flowers in southern Finland (Lindholm 1982). Since the flowers are self-compatible and easily self-pollinated, the seed production is primarily reduced by spring frosts but also perhaps by the lack of pollinators (Lindholm 1982). The size of the yield depends on the number of flowers. As flowers are formed in the year preceding fruiting, the yield is also dependent on the weather conditions in the previous year (Warming 1908; Flower-Ellis 1973, 1980). The coriaceous leaves, their silvery-glaucous lower surface and their revolute margins could indicate frost and drought resistance (Barvaux 1958). The slender, far-reaching subterranean rhizomes have long internodes, bear scale-leaves, and have a straight apex. The roots produced by the rhizomes are very slender and abundantly branched; they arise from the axils of the leaves (Warming 1908). The year's shoots have scale-leaves at their base. The axillary buds are partly protected by the erect petioles. The more vigorous of the lateral shoots arise from the axils of the uppermost leaves, i.e. those below the terminal inflorescence, and the uppermost shoot often forms a sympodium together with the parent stem (Warming 1908). On average, the below-ground biomass in mire ecosystems is known to be considerably higher than that above-ground (ratio 1:3–1:6; Flower-Ellis 1980; Wallén 1986; Malmer & Wallén 1986; Backéus 1990). Roots of A. polifolia may reach a depth of 45 cm in northern Sweden, with a ratio closer to 1:6 than to 1:3 (Flower-Ellis 1980). Andromeda polifolia has even more of its biomass below-ground: it reaches 75% (Malmer & Nihlgaård 1980; Malmer & Wallén 1986) and Wallén (1986) reports up to 98%. The erect-growing above-ground shoots develop from the terminal end of sparingly branched, vertically orientated rhizomes. Rapid shoot growth soon after the beginning of the growth period (May) was observed (Lindholm 1982). The mean above-ground biomass of 28 g m−2 would give a root and rhizome biomass of 168 g m−2 to a depth of 45 cm assuming a 1:6 ratio (Flower-Ellis 1980). The plant shows no measurable fine root activity below 10–15 cm. At the 2.5–5 cm level as much as 50% of total dry mass was vascular plant material, most of which was of fine root mass (up to 370 g m−2) (Wallén 1986). The fine roots thus formed 24 ± 4% of the total below-ground biomass (Wallén 1986). The mean length of leaves of all four generations was 8.53 ± 0.14 mm (Flower-Ellis 1980). There were in all 7200 ± 1844 leaves m−2 (Flower-Ellis 1980). The leaf area index (LAI) was 0.0855 ± 0.0244 in mid-season in northern Sweden (Flower-Ellis 1980). With 1008 live tillers m−2, this would represent 0.85 cm2 per tiller, shared mainly between leaves from 2 years (older leaves being few in number) (Flower-Ellis 1980). Fresh weight per leaf is 10.0–14.7 mg with a leaf area of 59.4–72.9 cm2 m−2 (Simonis & Hirsch 1962). Dry weight reaches 2–4 mg for current-year leaves and 3–4.5 mg for older leaves, with a leaf area ranging from 0.25 to 138.5 cm2 m−2 (Flower-Ellis 1980). LAI at the end of the growing season is as follows: current-year leaves 0.0444, 1-year leaves 0.0180, 2-year leaves 0.0020, assuming a mean leaf length of 8.53 mm with corresponding projected area as low as 11.9 mm2 in northern Sweden (Flower-Ellis 1980). The water content of the leaves reaches 54.1% (Tamas et al. 1975); values given by Simonis & Hirsch (1962) are 55.0–57.2%. The 2-year leaves are both less active photosynthetically and heavier than the younger leaves; the weight difference is most probably the result of the storage of reserves, possibly also of structural and other changes (Flower-Ellis 1980). One-year leaves from flowering tillers were lighter (at least 7%) than those from non-flowering tillers (Flower-Ellis 1980). The leaves are devoid of trichomes, but are covered with thick epicuticular waxes (Warming 1908). Stomata occur only on the lower surface (543.2 ± 24.6 mm−2; n = 12) of the leaves (A.-L. Jacquemart, unpublished data). Most Ericaceae are characterized by the presence of ericoid mycorrhizal infection (Cullings 1996), as recorded in A. polifolia (Harley & Harley 1987). The fungus normally involved in the infections is the ascomycete Hymenoscyphus ericae (Read) Korf & Kernan or its anamorphs (Pearson & Read 1973a; Harley & Harley 1987; Read & Kerley 1995). There are numerous, largely unsubstantiated, claims of the involvement of other fungi in the formation of ericoid mycorrhiza. Members of the genus Bisoascus and its anamorphs Oidiodendron are most frequently reported to be so involved, and there is evidence to support the view that they may be mycorrhizal under some circumstances (Read & Kerley 1995). Two fundamental roles of the mycorrhiza can be recognized, one involving detoxification of the soil environment, the other acquisition of essential nutrients, primarily nitrogenous (Pearson & Read 1973b; Kerley & Read 1995; Read & Kerley 1995; Cullings 1996) and phosphatic compounds (Harley & Harley 1987). Chamaephyte. The aerial shoots branch and the buds over-winter. Andromeda polifolia is under-represented in the seed banks of soils wherever it is common. Extremely rare germinants were observed in England (J.P. Grime, personal communication) and in Belgium. The basic chromosome number in Andromeda species is 2n = 48 (Fl. Eur. 3; Fl. Br. Isl.; Oberdorfer (1983); Uotila & Pellinen 1985). Andromeda polifolia showed positive photosynthesis from immediately after snowmelt in May, until mid-September in Sweden (Johansson & Linder 1975). The current-year leaves developed during late June, and from the middle of July their photosynthetic rates exceeded those of the 1-year-old leaves, both on a leaf area and on a dry weight basis (Johansson & Linder 1975). The photosynthetic assimilation has been calculated to be 0.6–0.8 mg CO2 h−1 g−1 dw for the 1-year-old leaves at the end of the growing season (1.0–3.6 mg CO2 h−1 g−1 dw for the current-year leaves) and 2.6–3.4 mg CO2 h−1 g−1 dw and 0.7–2.9 mg CO2 h−1 g−1 dw, respectively, for old and current-year leaves at the beginning of the season (Johansson & Linder 1975). The seasonal photosynthetic assimilation of evergreen leaves has been calculated to be 4–10 g CO2 (g leaves)−1 year−1 (Karlsson 1986). The seasonal carbon gain could thus be estimated to 0.06–0.14 g CO2 (g biomass)−1 (Karlsson 1986). Starch varied between 4.5 and 9.5% of dry weight and total carbohydrates between 9.1 and 14.9% in 1-year-old leaves (Flower-Ellis 1980; in the same Swedish site). Starch maxima occurred at noon, indicating that there was some accumulation in the leaves, mainly during the first half of the day (Flower-Ellis 1980). Cumulative diurnal dry weight equivalents of CO2 fixation reached 0.126 mg standard leaf−1 day−1 for current-year leaves, 0.132 for 1-year leaves and 0.106 for 2-year leaves (Flower-Ellis 1980). There was a simultaneous increase in the starch content of the 1-year leaves (0.25 mg leaf−1, 174 mg dm−2) and a small increase in the sugars, together (0.26 mg leaf−1, 180 mg dm−2) commensurate with the dry weight equivalent of assimilation during the period (0.25 mg leaf−1, 172 mg dm−2) (Flower-Ellis 1980). Thus 49% of the change in weight was accounted for by change in carbohydrate content. Similarly, variation in starch alone accounted for about 36% of the variation in dry weight (Flower-Ellis 1980). Therefore dry weight change and changes in starch and carbohydrates are associated, but the greater part of the weight variation cannot be accounted for by changes in starch and total carbohydrates. The residual leaf weight continued to show variation with time, over a range of 0.68 mg leaf−1 (472 mg dm−2). This difference should be attributable to translocation. This translocation from the leaf might be estimated as 0.44 mg leaf−1 (305 mg dm−2). During the growing season, current-year leaves gained 0.12–0.15 g m−2, 1-year leaves lost 0.73–0.97, 2-year leaves lost 0.14–0.29 (Flower-Ellis 1980