Galium aparine L.

Abstract

Galium L., Section KOLGYDA Dumort. (Section Aparine Koch). An annual herb with prostrate or, more usually, scrambling-ascending diffusely branched stems 15–300 cm, stout and hairy at the nodes, the four angles very rough with downwardly directed prickles. Leaves 12–60 × 3–8 mm, in whorls of 6–9, narrowly to widely oblanceolate or elliptical, mucronate, 1-veined, glabrous or with hooked bristles above, margins rough with backward-pointing prickles. Flowers 1.5 mm diameter in 2–5-flowered axillary cymes, their peduncles topped by a whorl of 4–8 bracts; hermaphrodite, sometimes male (andromonoecious). Calyx a minute annular ridge; corolla 1.5–1.7 mm in diameter, whitish, with four acute lobes. Stamens 4, exserted; styles 2, short, connate below; stigmas capitate. Two-seeded fruits with length of longest axis 3–5 mm (excluding setae), wider than the corolla, olive or purplish, covered with white hooked setae with tuberculate bases, their stalks divaricate. Mature fruit a dry mericarp with length of longest axis 2–3 mm, and a mean air-dry mass of 9.65 mg ± 0.33 (10 samples of 100 from a hedgerow population). Salisbury (1974) reports the average mass of seed from shade-tolerant woodland and hedgerow plants as 3.7 mg, and Grime et al. (1988) record a mean seed mass of 7.25 mg for a hedgerow population. Galium aparine is a highly variable species owing to a combination of phenotypic plasticity and genecological variation. The species has different responses to the environment corresponding to different environmentally conditioned life cycles [see VI (e)]; plasticity in the timing of seed germination, productivity, growth form, freezing tolerance, and the light and temperature dependence of photosynthesis enable G. aparine to establish itself in a wide variety of habitats. Potential variability concealed in the higher polyploid conditions, especially in the widespread hexaploids [see VI (d)], enabling them to respond to changing environmental conditions, is probably also the basis of their success. Among plants of G. aparine raised from seed collected from various sites in continental Europe, Böcher et al. (1955) distinguished at least five different climatic ecotypes or races that either may be discrete or more probably ranges of a large clinal variation: mediterranean, summer-annual (seed germinates in the spring) with accelerated development from Portugal; mediterranean, biennial from Spain; southern, winter- to summer-annual from France; northern, rather late flowering winter- to summer-annual from Denmark and Poland; and northern, very late flowering winter-annual (seed germinates in autumn) from Denmark and Sweden. Ecotypes of G. aparine have been demonstrated by Berkefeld (1988), differing in shape of cotyledons, hairiness of stems, colour of stem edges and length of fruit spines in plants grown under uniform garden conditions from seed collected in several different habitats. In Britain, two discrete ecotypes of G. aparine exist, one found in arable fields or open situations and the other growing in hedgerows ( Froud-Williams 1985); the two ecotypes are very similar morphologically but differ markedly in seed dormancy and germination requirements [see VIII (d)]. Bain & Attridge (1988) provide evidence of genotypic differences in shade strategies between hedgerow and field populations [see VI (e)]. Two forms have been recognized, the rarer G. aparine f. intermedium Bonnet, with smooth or tuberculate fruits without spiny hairs, and the common form G. aparine f. aparine with spiny fruits ( Moore 1975). Variants of G. spurium with setose fruits, apart from the flower characters and the diploid chromosome number, are often not easy to distinguish from G. aparine and have been described as G. spurium ssp. infestum ( Hanf 1983). Galium aparine is native on maritime shingle beaches, in primary tall-herb fen communities, and in primary alderwood in natural hydrarch successions, but is also a very variable cosmopolitan weed found in hedges, waste places, drained fen peat, on limestone scree, roadside verges, river and stream banks, and is a major arable weed, especially of cereal crops. Galium aparine is abundant throughout the British Isles; it occurs in all vice-counties ( Fig. 1). It is widespread throughout Europe ( Fig. 2), northwards in Norway to 70 °N, but otherwise absent from the region within the Arctic Circle, and southwards to the Mediterranean, west to the Azores and east to the Ural mountains. The distribution of Galium aparine in the British Isles. Each dot represents at least one record in a 10-km square of the National Grid. Mapped by Mrs J.M. Croft, Biological Records Centre, Institute of Terrestrial Ecology, mainly from records collected by members of the Botanical Society of the British Isles. (○) pre-1950: (●) 1950 onwards. The main distribution of Galium aparine in Europe and western Asia (modified from Vergl. Chor.). The base map is reproduced by permission of the Committee for the Mapping of the Flora of Europe (the bold dashed line shows the limits of Europe). Outside Europe G. aparine occurs eastwards to western Siberia, southern Siberia, western Asia and Turkestan, and southwards to the north-west African coast from Morocco to Tunisia. It is found between 30 °N and 48 °N in the eastern United States and along the western coast of North America from California northwards to southern Alaska. The altitudinal range of G. aparine in the British Isles extends from sea level to 366 m in Yorkshire (Alt. range Br. Pl.) to an upper limit of approximately 430 m at Nenthead, Cumbria ( Halliday 1997). Galium aparine is more abundant in lowland habitats, decreasing progressively at higher altitudes in the British Isles. In Europe it has a wide climatically determined range, from boreal oceanic–suboceanic conditions in the north through the temperate zone to a mediterranean climate in the south (Vergl. Chor.). The native distribution of G. aparine is given as European temperate but now widely naturalized and circumpolar temperate by Preston & Hill (1997). It occupies a niche with a seasonally contrasting light and temperature climate. In common with Urtica dioica, a species with which it is closely associated, G. aparine thrives on soils rich in available nitrogen ( Ellenberg 1988). However, it has been demonstrated by Pigott & Taylor (1964) that the supply of phosphate in combination with nitrogen is a major factor limiting the distribution of G. aparine; in response to additions of fertilizer nitrogen and phosphorus to pots of soil collected from under dominant Mercurialis perennis in Buff Wood, East Hatley, Cambridgeshire, UK, where G. aparine rarely occurs, the mean dry weight of seedlings of G. aparine after 55 days was 257 ± 14 mg with stunted leaves and no flowers without added fertilizer, 330 ± 17 mg with added nitrogen, 264 ± 25 mg with added phosphorus, and 587 ± 86 mg with vigorous growth and both flowers and fruits developed when nitrogen and phosphorus were supplied together. Galium aparine occurs widely in a range of habitats in association with mildly acid to ± base-rich damp to fairly wet soils. Grime et al. (1988) record that G. aparine is most frequent and abundant in soils between pH 5.5 and 8.0. It is abundant in scrub and occasional in hedges on chalk soils of pH 7.8 in Wiltshire (Fl. Wilt.). Galium aparine has been used successfully as a bioassay plant in a laboratory experiment with chalk grassland soils by R.A. Reed and P.J. Grubb (unpublished data). They obtained evidence of a succession of primary limiting nutrients, first phosphate when the freely diffusible nitrate was taken up from the total available soil volume more rapidly than the immobile phosphate, then nitrate as root competition became effective for the mobile nitrate but not for the immobile phosphate (cited by Bonis et al. 1997)****[see also VI (e) for supporting evidence]. Galium aparine shows a high degree of constancy in two types of shingle beach vegetation found on the north and west coasts of Scotland ( Gimingham 1964): in Atriplex glabriuscula–Silene maritima (uniflora)–Tripleurospermum maritimum stands occurring on fringing beach composed of pebbles set in a sandy matrix with an admixture of algal debris, where shingle movement is confined to winter; and on apposition banks to landward of the foreshore in Arrhenatherum elatius stands, especially on the Isle of Arran. Galium aparine is also a component of shingle vegetation at Dungeness and in Wales ( Scott 1963). Both U. dioica and G. aparine are very abundant in fen carr in the region of the Broads in east Norfolk and in the valley fenwoods of Breckland (Tansley, Br. Isl.). Galium aparine was one of 20 species recorded most frequently in 121 Wiltshire hedges (Fl. Wilt.). From detailed botanical data on the composition of hedgerows collected during countryside surveys in Britain in 1978 and 1990 ( Barr et al. 1993 ), the cover of G. aparine in paired plots increased highly significantly (P < 0.001) between 1978 and 1990, with a mean difference between percentage cover in the 2 years of 5 ± 1.1 in a sample of 172 plots ( Bunce et al. 1994 ). The following phytosociological account is based on the National Vegetational Classification ( Rodwell 1991, 1992, 1995, 1999). The joint constants of the Matricaria maritima (Tripleurospermum maritimum)–Galium aparine strandline community (SD3), together with Atriplex glabriuscula and Stellaria media, are the most prominent and frequent elements in the generally open and often patchy strandline vegetation confined to Scotland and along sheltered shores in north-west England. Apart from the two constants in Phragmites australis–Urtica dioica tall-herb fen (S26), G. aparine is the only species that is frequent throughout; locally in the Filipendula ulmaria subcommunity, G. aparine is prominent together with the other constants Phragmites or U. dioica or F. ulmaria; the A. elatius subcommunity dominated by Phragmites has varying amounts of U. dioica and G. aparine and, beneath, tussocks of A. elatius, with scattered plants of Cirsium arvense and Heracleum sphondylium very characteristic of this vegetation. The community occurs throughout the lowlands but especially in Broadland, east Norfolk, the Fens and around the Shropshire and Cheshire meres; the Filipendula subcommunity, however, has only a scattered distribution and the Arrhenatherum subcommunity is most frequent in south-west England and south Wales. Galium aparine is a common species in three woodland and scrub communities: Alnus glutinosa–Urtica dioica woodland (W6), where it is a joint constant in the typical subcommunity, widespread but local throughout the lowlands, occurring where active alluvial deposition is taking place on more mature rivers and on the remnants of undrained flood plains and eutrophicated mires; Crataegus monogyna–Hedera helix scrub (W21), where it is very common in the Hedera helix–Urtica dioica subcommunity in which Crataegus monogyna, Rubus fruticosus agg., Hedera helix and U. dioica are constant species, widely distributed through the British lowlands, and also in the floristically richer Mercurialis perennis subcommunity, found on heavy-textured base-rich soils especially in areas with clays and shales; and the Rubus fruticosus–Holcus lanatus underscrub (W24), where it is a constant in the Arrhenatherum elatius–Heracleum sphondylium subcommunity that is consistently enriched by a very distinctive group of preferentials, A. elatius, Festuca rubra, U. dioica, H. sphondylium and Taraxacum officinale agg., which are constants, and frequently Anthriscus sylvestris and Chaerophyllum temulentum (temulum), especially characteristic of this kind of vegetation which is ubiquitous on suitable soils throughout the British lowlands. Galium aparine, together with Oxalis pes-caprae and Sonchus oleraceus, is preferential in the Cerastium glomeratum–Fumaria muralis ssp. boreai community (OV6) Vicia hirsuta–Papaver dubium subcommunity, confined to regularly disturbed fertile, light, non-calcareous soils cultivated for bulb and vegetable production in the extreme oceanic climate of the far south-west of Britain, in Cornwall and The Scillies; it is also preferential in the Stellaria media–Capsella bursa-pastoris community (OV13) in the Urtica dioica–Galium aparine subcommunity, which occurs widely on fertile loamy soils, as weed vegetation among root vegetable, salad and cereal crops, throughout the British lowlands; and is a joint constant in species-poor tall-herb vegetation dominated by densely abundant U. dioica, described as a Urtica dioica–Galium aparine community (OV24), in nutrient-rich, moist but well-aerated, disturbed soils throughout the lowlands. Galium aparine occurs frequently in two maritime communities: Hippophae rhamnoides scrub (SD18), in the Urtica dioica–Arrhenatherum elatius subcommunity, on dunes on the east coast between Kent and Fife, especially in Lincolnshire and north Norfolk; and Brassica oleracea maritime cliff-edge community (MC4) Beta vulgaris ssp. maritima subcommunity, in more maritime conditions on crumbling edges and sloping ledges of south-facing cliffs in calcareous rocks on the south coast of England. Galium aparine occurs frequently in Alnus glutinosa–Fraxinus excelsior–Lysimachia nemorum woodland (W7), in the Urtica dioica subcommunity which is widely, although locally, distributed throughout the upland fringes of the north and west; in Fraxinus excelsior–Acer campestre–Mercurialis woodland (W8), in the Geranium robertianum and Allium ursinum subcommunities, both especially characteristic of the Yorkshire and Derbyshire Dales and the Welsh Marches; in Prunus spinosa–Rubus fruticosus scrub (W22), which is of widespread distribution through the British lowlands on mesotrophic mull soils of moderate base status; and is also frequent in Pteridium aquilinum–Rubus fruticosus underscrub (W25) in the Hyacinthoides nonscripta subcommunity commonly widespread on suitable soils throughout lowland Britain. In and around roadside and field ditches throughout lowland Britain, G. aparine frequently occurs in Arrhenatherum elatius grassland (MG1) Filipendula ulmaria subcommunity; it is occasional to scarce in Arrhenatherum elatius–Filipendula ulmaria tall-herb grassland (MG2), confined to scattered localities in northern England on the Carboniferous limestone of Derbyshire and Craven; and scarce in Festuca rubra–Agrostis stolonifera–Potentilla anserina grassland (MG11), a lowland vegetation type frequent near sea level, where it occurs as extensive stands in the flood-plains of major rivers and on the upper salt-marsh. Galium aparine occurs frequently in the Papaver rhoeas–Silene noctiflora community (OV16), in light to well-drained calcareous soils, mostly among cereals, across the warmer and drier south-east of England from Dorset and Wiltshire, north-east to Lincolnshire; and in the Epilobium hirsutum community (OV26) Filipendula ulmaria–Angelica sylvestris subcommunity, common in ditches along roadsides, widespread and common throughout the British lowlands. Galium aparine is occasional to scarce in a number of woodland communities: Salix cinerea–Betula pubescens–Phragmites australis woodland (W2) Alnus glutinosa–Filipendula ulmaria subcommunity largely confined to East Anglia and some of the Cheshire and Shropshire meres; Alnus glutinosa–Carex paniculata woodland (W5), especially in the Phragmites australis subcommunity widely distributed in the Shropshire and Cheshire meres; in Fraxinus excelsior–Sorbus aucuparia–Mercurialis perennis woodland (W8), distributed in the cooler and wetter north-western parts of Britain; and Fagus sylvatica–Mercurialis perennis woodland (W12), especially in the Sanicula europaea subcommunity characteristic of the scarps of the North and South Downs, the Chilterns and the western end of the Cotswolds. Galium aparine is occasional in several open communities: Papaver rhoeas–Viola arvensis community (OV3), annual weed vegetation widespread in the southern part of Britain; Veronica persica–Veronica polita community (OV7), characteristically a weed community of cereals and other annual field crops on lighter, well-drained soils in the lowlands of south-eastern and eastern Britain; Veronica persica–Alopecurus myosuroides community (OV8), a similar weed community but on wetter heavy-textured soils, around the Fenland fringes and scattered west to Dorset; Anagallis arvensis–Veronica persica community (OV15), an annual weed community, usually dominated by ephemerals, found in cereal crops on base-rich soils in south-east England; and Parietaria diffusa community (OV41), which occurs in crevices and on small ledges in walls and on rock faces in quarries and natural cliffs in the lowlands of southern England. Galium aparine is scarce in three maritime communities: on the foreshore in Leymus arenarius mobile dune community (SD5); in Elymus pycnanthus (Elytrigia atherica) salt-marsh (SM24); and in Elymus (Elytrigia) repens salt-marsh (SM28). Galium aparine is scarce in a number of swamp communities: Carex paniculata sedge-swamp (S3); Phragmites australis swamp and reed-beds (S4), Phragmites australis subcommunity and Atriplex prostrata subcommunity, with a patchy distribution on coastal and inland salt-marshes; Glyceria maxima swamp (S5); Carex riparia swamp (S6); Carex acutiformis swamp (S7); Carex pseudocyperus swamp (S17); Carex otrubae swamp (S18); Scirpus (Bolboschoenus) maritimus swamp (S21), Atriplex prostrata subcommunity and Agrostis stolonifera subcommunity. Galium aparine is also scarce in two tall-herb fen communities: Phragmites australis–Eupatorium cannabinum tall-herb fen (S25); and Phalaris arundinacea tall-herb fen (S28), Phalaris arundinacea subcommunity and Epilobium hirsutum–Urtica dioica subcommunity. Galium aparine is scarce in several woodland communities: Salix cinerea–Galium palustre woodland (W1); Salix pentandra–Carex rostrata woodland (W3); Quercus robur–Pteridium aquilinum–Rubus fruticosus woodland (W10); and Quercus petraea–Betula pubescens–Oxalis acetosella woodland (W11). Galium aparine is also scarce in a number of weed communities: Poa annua–Senecio vulgaris community (OV10); Polygonum aviculare–Chamomilla suaveolens (Matricaria discoidea) community (OV18); Lolium perenne–Dactylis glomerata community (OV23); and Epilobium (Chamerion) angustifolium community (OV27). In continental Europe G. aparine is described as having accompanied cultivation since the Neolithic, often with U. dioica, and is a character species of the class Artemisietea (Pfl. Exk.), especially in subclass Galio-Urticenea in the order Convolvuletalia and order Glechometalia ( Oberdorfer 1983), and in the persistent nitrophilous ruderal vegetation of woodland edges in the alliance Geo-Alliarion referred by Ellenberg (1988) to the order Calystegio-Alliarietalia (Convolvuletalia); it also occurs with high frequency in the subclass Artemisienea vulgaris in the order Artemisietalia ( Oberdorfer 1983). Galium aparine occurs with high frequency in arable-weed communities on damp soils in the class Secalinetea (Pfl. Exk.; Oberdorfer 1983); and with high constancy in lowland flood plain woodlands in central Europe dominated by willow, poplar, elm or oak in the alliance Salicion albae (Pfl. Exk.; Ellenberg 1988). In the submediterranean-central European region, G. aparine is a differential species in the important scrub and hedgerow association Prunus spinosa–Carpinus betulus, referred to the alliance Prunion spinosae. It also occurs with high constancy in the Galio-Carpinetum association found on soils influenced by ground water in oak–hornbeam woods ( Ellenberg 1988). In the humid mountainous regions of mediterranean France, G. aparine is frequent in the woodland association Alneto-Fraxinetum oxycarpae referred to the alliance Alneto-Ulmion, which forms thickets along river banks where it is subjected to periodic inundations ( Braun-Blanquet 1951). In the Netherlands, Westhoff & den Held (1969) record G. aparine in a number of communities: in Oxalido-Chenopodietum polyspermi (Chenopodietea) ruderal communities in gardens, nurseries and in moist to wet riverbank situations; common in the alliance Galio-Alliarion (Artemisietea); a member of the characteristic species combination of the Angelicion litoralis ruderal community around estuaries; a member of the characteristic species combination of the Epilobium hirsutum society; in Salicetum triandro-viminalis, a differential of subassociation rubestosum, and in Salicetum albo-fragilis, a differential of subassociation cardaminetosum, both in the class Salicetea purpureae; and also in the Alno-Padion of Quercetea robori-petraeae woodlands. Whilst G. aparine is an annual dicotyledonous weed of seemingly ubiquitous occurrence in hedgerows, it has increasingly become of widespread importance as a weed of arable crops. In a survey of arable dicotyledonous weeds, G. aparine was the second most frequent broad-leaved weed present at harvest, while it was the most frequent weed of winter wheat, occurring in 12% of crops surveyed ( Chancellor & Froud-Williams 1984), and was present in 57% of 450 fields of winter oilseed rape surveyed just prior to the summer harvest in nine areas of central southern England ( Froud-Williams & Chancellor 1987). Despite the apparent association of G. aparine with early sown winter cereals established by minimal cultivation, there is no evidence to suggest that weed problems are exacerbated by direct-drilling per se, although shallow cultivation may increase germination and provide more suitable conditions for establishment; as many as 44% seedlings of G. aparine may develop following tine cultivation compared with direct-drilling (29%), while substantially fewer seedlings emerge after ploughing. Formerly, straw-burning could provide an effective means of control, destroying more than 90% of seeds on the soil surface ( Froud-Williams 1985). Ripe seeds of G. aparine collected from plants growing in a field margin were sown in soil at various depths in wooden boxes in an outdoor experiment ( Froud-Williams et al. 1984 ); emergence was virtually confined to the period October–January; compared with surface-sown seed, burial over a range between 5 and 100 mm depth increased germination and emergence of the large-seeded G. aparine. The effects of G. aparine on crop production have been reviewed by Froud-Williams (1985), namely the competitive ability of G. aparine, interference with harvesting and crop contamination; interspecific competition resulted in yield losses from winter wheat of 30%, 47% and 52% at experimental densities of 25, 100 and 520 G. aparine plants m–2, and yield losses from spring barley of 19%, 42%, 55%, 70% and 80% at densities of 35, 132, 309, 619 and 1190 G. aparine plants m–2; the effect of lodging of cereals by G. aparine can reduce yields by 30–60%; up to 21% of samples of cereal seed can be contaminated by seed of G. aparine. A replicated randomized glasshouse experiment was carried out by Lintell-Smith et al. (1992) to determine the hierarchy of competitive ability of spring wheat (Triticum aestivum cv. Tonic), Anisantha (Bromus) sterilis, G. aparine and Papaver rhoeas at four nitrogen levels at rates equivalent to 0, 75, 150 and 300 kg N ha–1 in the form of a slow release fertilizer. For each of the 16 treatments (four species × four nitrogen levels) a target plant of wheat was set in the centre of each 11.5-cm diameter pot filled with John Innes No. 1 compost, and surrounded by three individuals of either wheat or of the individual weed species. The competitive hierarchy of the four species in suppressing the total ear weight of the target wheat plant at the highest nitrogen level fell in the order wheat > A. sterilis > G. aparine > P. rhoeas. Irrespective of the species of neighbouring plant, the total ear weight of the target wheat plant increased with the level of soil nitrogen. Consideration of the relative competitive abilities of the species in relation to the strongest competitor (wheat) indicated that, as the level of nitrogen increased, the weeds became more competitive in relation to wheat. Biomass, plant size, plant density and the inequality of sizes were assessed for autumn-emerging roadside populations dominated by G. aparine during early stages of growth by Puntieri & Hall (1996). One study showed that the slope of the log–log size–density relationship for all plant species present in samples was closer to –1.5 (as predicted by the 3/2 power law of self-thinning) and that for G. aparine was closer to –1.0 in five separate populations. The size inequality of G. aparine tended to increase or to remain constant during periods of high mortality, and in early harvests it was negatively related to population density. In a second study there were simultaneous decreases of both biomass and density of G. aparine and all plant species during a period of a month soon after emergence, and a higher size inequality of G. aparine in those patches where plant density (and that of G. aparine) was lower. Labelling of seedlings of G. aparine, belonging to different cohorts of emergence, indicated density-dependent mortality and a higher probability of survival for seedlings emerging very early. Galium aparine seems to have a weak size hierarchy development and limited individual growth at high population densities. Galium aparine is effectively controlled with DNOC and MCPP herbicides ( Salisbury 1964). In cereal crops it is susceptible at the early seedling stage to the use of mecoprop salt, dichloroprop salt, dinoseb, benazolin, bentazone and MCPA mixtures (Weed Handbk.). The pre- and early post-emergence herbicidal activity of diflufenican (N-2,4-difluorophenyl-2–3-trifluoromethylphenoxy-3-pyridinecarboxamide), a novel herbicide, is reported by Cramp et al. (1987) and attention is drawn to its ability to control important weeds in winter cereals, including G. aparine, which is resistant to substituted-urea herbicides. The results of a series of 11 field experiments over two seasons ( Lutman et al. 1988 ) indicated that the control of G. aparine in winter cereals was most effective when mecoprop and a proprietary mixture of ioxynil + bromoxynil was applied between December and March (up to 90%). But when mecoprop was applied alone in April, especially when soil temperatures were > 6 °C, control was increased to 94%. Galium aparine is locally capable of developing dense populations consisting of a large number of discrete individual seedlings; it is commonly present in ephemeral assemblages of enriched disturbed land and in some woodland, scrub and tall-herb communities (see III), where it can keep pace in height growth with established perennials. Seasonal changes in the above-ground biomass of G. aparine have been determined in various stands of vegetation by Al-Mufti et al. (1977) . The mean maximum biomass values, which occurred in the month of June, in 0.25-m2 samples, as g m–2 ± standard error (number of replicates), were: 56 ± 25 (5) within a stand of U. dioica on alluvial soil in Lathkilldale, north Derbyshire; 29 ± 7.5 (4) within a stand of Chamerion (Chamaenerion) angustifolium on a brown earth in Lathkilldale; 5 ± 1.8 (5) in a woodland clearing under U. dioica on alluvium in Totley Wood, Sheffield, South Yorkshire; and 20 ± 5 (10) under the tree canopy within a stand of U. dioica on alluvium in Totley Wood. The mean aerial biomass of G. aparine sampled in late July, in nine random 1-m2 samples of roadside Arrhenatheretum in south-eastern Cambridgeshire, was 2.4 ± 1.2 g m–2 ( Grubb 1982). Plasticity of growth and of biomass allocation was investigated by Auge & Mahn (1988) in three populations of G. aparine in spring-germinating plants in their native habitats, an arable field south-west of Halle, in Fraxino-Ulmetum tilietosum forest, and in Populus×canadensis forest, both south of Leipzig, Germany. Ontogenetic drift of relative growth rate, biomass allocation as well as biomass and seed production were closely related to the light factor, differing between the three ecosystems. Allocation between vegetative and reproductive growth was characterized by a complete switch at the start of the reproductive phase in the most light-limited forest population and by a large overlap under more favourable conditions in the arable field population. Biomass allocation among the vegetative organs was strongly dependent on total biomass of the individuals. Multivariate comparisons revealed that the entire allocation patterns of the forest populations were rather similar at the date of peak vegetative biomass, but differed substantially from the arable population. Some of the observed differences between populations seemed to be due to phenotypic plasticity. The seasonal course of frost tolerance in potted autumn-emergent seedlings of G. aparine has been measured by Kutsch & Kappen (1990); frost tolerance (the temperature that would result in a 20% mean death of shoots) from mid-October to mid-November was –7 °C, increasing by the end of November to –10 °C and to a limit of –17 °C by early December, then decreasing to –9 °C in March and –2 °C in April. The net photosynthetic response to light and temperature did not shift during the period December to March, with an optimum temperature for photosynthesis of 15 °C and a net photosynthetic rate of 8.1 mg CO2 dm–2 h–1. During this winter period freezing and undercooling temperatures fluctuated around –3 °C in the assimilatory tissues. Down to –3 °C no frost-induced decrease of net photosynthesis was observed, but below this temperature ice was formed in the leaf mesophyll and photosynthesis ceased. CO2 uptake was apparent within a few hours after thawing; below –5 °C the rates were reduced depending on the severity of the preceding frost. Photosynthetic pr