Characteristics Distinguishing Invasive Weeds Within Echium (Bugloss)

Weerl Re.seareti. 1986, Volume 26. .151-364

Characteristics distinguishing invasive weeds within Echium (Bugloss)

F, FORCELLA. J. T. WOOD AND travers le monde de la propagation des vegetaux S. P. DILLON * North Central Soil Research etrangers: cependant, les systemes de quarantaine Laboratory, USDA-ARS. Morris MN 56267. n'ont pas ete etablis exclusivement sur des criteres U.S.A., and *CSIRO-Austratia Divisions of objectifs. Des etudes d'epidemiologie compara- Mathematics and Statistics, and Ptant Industry, tives pour des adventiees etrangeres connues Canberra ACT 260] peuvent fournir de tels criteres et ainsi accroitre le succes dc la mise en quarantaine des vegetaux. Pour cette raison. des donnces biogeographiques Accepted 28 February 1986 et ecophysiologiques ont ete regroupees et analy- sces pour le genre Echium (Boraginacee). en particulier pour trois especes de mauvaises herbes differemment reparties en Australie: E. itaticum Summary: Resume: Zusammenfassung L. (rare), E. vutgare L. (peu repandu), E. ptantagineum L, (eommun). Parmi ces donnees. on trou- Plant quarantine agencies attempt to regulate the vait les suivantes: repartition originelle en Eurasie continuing worldwide problem of spread of alien et en Afrique du Nord, historique de la propaga- plants, but systems of plant quarantine have not tion en Australie. germination des semences, been based entirely on objective criteria. Com- croissance vegetative et propension a fleurir. Les parative epidemiological research of known alien caracteristiques quantifiables qui permettraient weeds may provide such criteria and thereby de distinguer les especes nuisibles d'Echium de improve the success of plant quarantine. For this leurs equivalents inoffensifs et dont les valeurs reason biogeographical and ecophysiological pourraient tres aisement etre determinees par les data were gathered and analyzed for Echium organismes officiels responsables des quaran- (Boraginaceae), especially for the three differen- taines sont: Pampleur de la distribution d'origine tially distributed and weedy species in Australia: et la rapidite de la germination des semences. Bien E. itaticum L. (rare), E. vutgare L. (uncommon). que ces resultats proviennent de seulement quel- and B. ptantagineum L. (common). Such data ques taxons. ils peuvent ctre appliques, en prin- included the following: native distributions in cipe. a de nombreuses especes. Eurasia and North Africa, historical spread in Australia, seed germination, vegetative growth and propensity to flower. Quantitative plant Merkmale zur Definition schadticher Arten in der characteristics which distinguish weedy species of Gattung Echium (Natterkopf) Eehium from their innocuous counterparts, and Pflanzenquarantaneamter versuchen das welt- whose values could most easily be determined by weite Problem der Ausbreitung von eingeschlep- plant quarantine officials, are the breadth of pten Pflanzen zu kontrollieren; die Quarantan- native distribution and rapidity of seed germina- evorschriften sind jedoeh nicht vollig auf objektiv tion. Although these results were derived from erfassbare Kriterien abgestutzt. Vergleichende only a few temperate taxa, they may apply in epidemiologische Erforschung von Adventiv- principle to many species. pflanzen kann derartige Kriterien liefern und damit den Nutzeffekt von Quarantanemassnah- men verbessern. Zu diesem Zweck wurden fur die Caraeteres distinctifs des mauvaises herbes enva- Gattung Eehium (Boraginaceen) biogeogra- hissantes dans le genre Echium phische und okophysiologische Daten gesammelt Des agences de mise en quarantaine de vegetaux und analysiert; es wurden dabei speziell die drei in s'attachent a controler le probleme permanent a Australien als Unkrater geltendcn und verschie- 352 F. Foreetta, J. T. Wood and S. P. Ditton den verbreiteten Arten E. itaticum L. (selten). Several plant traits have been presumed to E. vutgare L. (gelegentilich vorkommend) und E. distinguish potentially troublesome alien species ptantagineum L. (haufig) untersucht. Der Daten- from innocuous plants (Baker. 1965), Some of katalog enthielt Angaben uber: die ursprungliche these may not be practical for use by plant Verbreitung in Eurasien und N-Afrika. Ges- quarantine officials, whereas others are valueless. chichte der Ausbreitung in Australien. Samenkei- For example, genetic diversity, although much mung, vegetatives Waehstum und Bluhbereits- discussed in the past (see Baker, 1974). has not chaft. Der Ausdehnungsbereich der been found to be associated with the ability of a ursprunglichen Vorkommen und die Geschwin- plant or animal to spread widely (Moran & digkeit der Samenkeimung sind quantitativ Marshall. 1978: Myers & Sabath. 1981; Jain, erfassbare. durch Quarantanebcamte leicht zu 1983: Forcella & Wood, i 984). In contrast, rapid bewertende, Kriterien zur Unterscheidung zwi- seed germination is an easily determined trait and schen unschadliehen und als Unkrauter schadli- one which appears to characterize widespread chen Eehium-XrX.cn. Obwoh! diese Ergebnisse nur noxious weeds. Narrowly distributed speeies von relativ wenigen, unter tempcrierten Be- exhibit relatively slow germination. This differ- dingungen vorkommenden, taxonomischcn Ein- ence in rapidity of seed germination between heiten abgeleitet worden sind. mogen sie im serious and minor weeds occurs both within a Prinzip fur viele Arten Gultigkeit haben. genus[e.g. A'afl?/j/«m(Martin»S:Carnahan, 1983)J and among genera (Forcella. 1985). A great deal of further research will be necessary for successful Introduction prediction of whether one plant species has the Most countries are hosts to increasing numbers of potential to be a serious weed whilst another does alien plants [e.g.. Australia (Specht, 1981)|, but not. and for reconciliation of which plant traits only some of these new introductions are likely to are most useful for screening hitherto unfamiliar become serious weeds (Forcella & Harvey, 1983), piant species. Towards this end we have com- How will potentially serious weeds be identified? pared the epidemiology of three closely related This is an important question, because only these alien plants in Australia. plants should merit expensive research and con- Three herbaceous species of the genus Echium trol programmes. Weed epidemiology is a subject L. occur in Australia (Piggin. 1977), E. ptantagi- which embraces this problem through determina- neum L., an annual or occassional biennial, has tions of (1) probabilities of plant introduction, naturalized so well that it is perhaps one of the establishment and further spread, and (2) modes most common and characteristic plants of large of transport of species with high probabilities of sections of southern Australia. F. vutgare L., a further spread. If successful, weed epidemiology biennial and occassional annual, is not wide- would facilitate development of quarantine and spread, but restricted to cool and moist sectors of control technologies prior to arrival and spread southeastern Australia, Lastly E. ttalicum L, is a of potentially troublesome species. very rare, short-lived perennial (Piggin, 1977). For solutions to the outstanding problems of What has allowed sueh differential infestation? plant quarantine, basic principles of weed epi- Have the two restricted species had too little time demiology must be developed and/or refined. to spread to their physiological limits, or are they Some tentative principles include: (1) species with incapable of thriving in areas other than where very broad native distributions have higher pro- they currently grow? We attempt to answer these babilities of introduction than those with narrow questions below, and we use our answers to help native distributions (Forcella & Wood. 1984). (2) build a conceptual model of successful and at least some taxonomic sets of serious weeds tend unsuccessful alien plants, especially in temperate to originate from the same small group of coun- environments. tries (Forcella & Wood, 1984). (3) aliens intro- Seemingly similar comparative work eon- duced at multiple sites are apt to spread at rates ducted by Baker and his students (see Baker 1974 higher than those with fewer sites of introduction and references therein) has provided much valu- (Auld & Coote. 1980). and (4) species with high able theoretical insight into differential migration initial rates of spread within a region typically of species of several taxa. However, these studies become the region's most troublesome weeds were rather qualitative, at least in their published (Forcella. 1985). forms, and the migrations they discussed often Characteristics of invasive weeds 353 referred to those which occurred in the Pleisto- Australian distributions cene, If tomorrow's plant quarantine decisions Rates of collection of Echium herbarium speci- are to be rigourous, then more quantitative mens through time {cf Lacey. 1957; Auld et al., evidence will be necessary on the epidemiology 1982/83) were calculated using label information and ecology of today's alien weeds. from Piggin (1977), In addition, we determined latitude and longitude of each specimen collection site and its appropriate 1 by 1-5 reference Methods map grid (Anon,. 1975; Scott& Kenneally. 1981). Distribution maps using these grids were then generated by computer (Chippendale & Wolf. A select group of variables bearing on the biogeo- 1980) for each decade from 1831 to 1977. graphy and ecology of Echium was analysed. Although the resulting time-series distribution These variables included distributions of the maps may not represent ranges of plants accu- species in their native continents as well as rately, they do refleet true distributions as pre- Australia and characteristics of seed germination. cisely as is possible. In any event, in the analyses vegetative growth and flowering, especially in which follow it is only the relative extent of relation to temperature and/or photoperiod. distributions among both time periods and spe- Other variables whieh were not examined may be cies which is important. We feel that herbarium as important as those which were. The measured specimens are adequate for this purpose. ecophysiological variables were derived from plants whose seeds originated from a single population for each speeies. We recognize that Seed germination such narrow genetic bases restrict our ability to Seeds of E. italicum were collected east of Cor- extrapolate. Nevertheless, as will become clear. owa. New South Wales (NSW), in January 1982. results for E. plantagineum closely match those Rarity of this species at the collection site and available in the literature for widely disparate elsewhere resulted in only 118 seeds being avail- populations of this species. Additionally, our able for experimentation. Abundant seeds of E. interspecific differences were often so large that vutgare were collected in May 1981 between intraspecific variability was considered unimpor- Bredbo and Cooma. NSW. Near Wagga Wagga. tant. NSW, quantities of E. ptantigineum were gathered in February 1982. All seeds were stored on laboratory shelves until used in September 1982 and January 1983. Storage duration should have Native distributions been sufficient for all after-ripening processes to Eurasian and North African countries, or prov- oecur (£•/, Ballard, 1970; Piggin. 1976). inces within large countries, in which any ofthe 17 species of European Eehium are known to occur E.xperiment I. Stored seeds of eaeh speeies were were recorded from the following sources: Davis weighed in three groups of 20 seeds each. Subse- (1978). Freinbrun-Dothan (1978). Gibbs (1972), quently, seeds were germinated in petri dishes in Jahandiez & Maire (1934), Klotz (1960), Post three environmental chambers with day/night (1933). Qaiser (1979), Quezel & Santa (1963), temperatures of 28 720 . 23/15" and 18710, Riedl (1967) and Tackholm (1974), A presence/ Each chamber received 8 h of natural daylight absence matrix of species/countries was con- supplemented with 4 h of incandescent light (60 tructed and subjected to correspondence analysis //E m"- s"'). Radicle emergence was monitored (Hill. 1973), whieh compared multivariately the daily. Three replicates of 25 seeds each were relationships among species according to their possible for E. ptantigineum and E. vutgare, but distributions, and relationships among countries only a single petri dish containing 36 seeds could according to their inhabitant species. First and be examined in each chamber for E. italicum. seeond principal components of resultant analyses for species and countries were superimposed Experiment 2. Ten petri dishes, each with 25 seeds upon one another. This allowed better visualiza- of both E. plantigineum and F. vutgare. were tion of association of species with particular aligned on a temperature gradient bar with a countries (Foreella & Wood 1984), constant temperature gradient ranging from 2'"' to 354 F. Forcelta, J. T. Wood and S. P. Dillon

32 \ Seeds were illuminated continuously with were introduced to Australia have the most fluorescent light (100/JE m"^s"')- Radicle emer- widespread native distributions ofthe 17 species gence was monitored daily in three replicates of analysed, occurring in 29, 27 and 34 countries or each dish. regions (£. italicum. E. vulgare and E. plantagi- Subsequently, we received a sample of F. neum. respectively). Species not known in Austra- ;7fl/;Vum seeds collected in September 1983 by J. F. lia occur in an average of 6-4 (±5 4) countries. Vayssieres at Lae du Salagou, Heiault, France. In This average is significantly (/*<001) smaller November, germination of these seeds was exam- than that ofthe 'Australian' species in parametric ined as above, except that the temperature gra- or nonparametric statistical comparisons. dient ranged from 10''-40^. We recognize that the Among the "non-Australian" species £. russicum genetie base of this seed population may differ has the widest distribution (19 regions), but is from Australian material. restricted mostly to eastern Eurasia. E. parviftora, the next most wide-ranging species (13 regions), Vegetative growth has a range seemingly similar to F. plantagineum but is more closely associated with the shores of One- to 3-day-old seedlings were transplanted the Mediterranean Sea. into pots (10 cm diameter, 20 cm deep) filled with perlite and sand (1:1). Pots were placed in one of Biogeographie relationships among Echium nine environmental chambers, each programmed spp, are shown in Figure 1. Species characteristic for one of nine combinations of day/night tem- ofthe Iberian Peninsula (E. albieans. E. boissierii, perature and photoperiod: 28'/20\ 23/15\ 18 / E. tusitanicum and £, rosutatum) form a discrete 10% 16 h, 12 hand 8 h. Photoperiods consisted of cluster. Nearby, but less distinct, is a north central 8 hr of natural daylight supplemented by an Mediterranean group which includes E. asperi- appropriate period of incandescent light (60 /JE num, E. creticum and E. sabulieola, and a western m"^ S"'). Plants were watered twice daily, once Mediterranean pair composed of F.Jlavum and £. with Hoagland's solution and once with water. tuberculatum. A strictly circum-Mediterranean Established plants were thinned to one per pot. group Is comprised of E. arenarium, E. angustifo- At weekly intervals from 3-6 weeks after tium and F. parviflora. Both F. italicum and E. transplantation four pots in each chamber of ptantagineum are very closely linked to this latter both E. plantagineum and E. vulgare were har- group, but the first speeies ranges more widely to vested. Leaf areas of these plants were deter- the south and east, while the second extends mined. Roots were washed free of soil and both farther north. E. vulgare is a northern plant, roots and shoots were oven-dried and weighed. which is unknown south ofthe Mediterranea Sea; For £. italicum silhouettes of intact leaves of four its northern limit is about 50 N latitude. plants from each chamber were constructed and In Figure I both Iberia and northern Europe their areas determined. stand alone, because of higb and low Echium diversity, respectively. Interestingly, central Euro- pean Mediterranean regions are more closely Flowering allied with North Africa than either is to Iberia. Four or more plants of each species were main- tained in the chambers from January 1983 until flowers were noticed, or until April for vegetative Australian distributions plants. At this time vegetative plants were repot- Currently, E. italieum has a disjunct distribution ted (30 cm diameter pots); half of these pots were in Australia (Fig. 2), occurring in southeastern placed in a greenhouse (25'/10') and the South Australia (Adelaide to Mount Gambier) remainder in a coldframe. Later, half the cold- and the border of north central Victoria and frame pots were transferred to the greenhouse. adjacent south central NSW. Additionally, the Plants were watered and fertilized as needed. rate of spread of this species has been and is still Flowering responses were noted. the lowest of the three Australian species (Fig. 5a). More widespread is E. vulgare (Figure 3). Although restricted to cool/humid portions of Results southeastern Australia, it ean be prominent along Native distribution the Great Dividing Range of NSW and Victoria, The three herbaceous species of Echium whieh as well as in Tasmania. This speeies appears to Characteristics of invasive weeds 355

2 2

CT EG 14 AG TU 1 MO GR '"ET LY 1^ ..TR SY 1, 9-.. ' ^0 SI •. ''sw*'- CR. - SA '•••._ '^E_j,j ^"^uc at 0 : 12 c o IT *•.,_ BR, C^£ a. 13 ^*FR '•'.. ••. HU eo o 6 '••-.15 PO ID -1 c; o B r 1 0L

-3 -

- 5

1 1 1 1 1 1 1 I 1 1 -2 0 First component Fig. 1 Correspondence analysis of Echium spp. (numbers) and North African and Eurasian regions (letters) in which they are native. The first and second components of Ihe analysis correspond to geographic gradients from south to north and wesi lo east, respectively. The three species occurring in Australia are represented by bold and enlarged numbers and connected by dotled lines. Regions characterizing various species are proximal lo such species in the graph. Appendix 1. Abbreviations for countries and regions shown in Fig. I: AB Albania, AO. Algeria, AU Austria, BA Balaeras Islands. BE Belgium. BL Baltic Islands. BR Britain. BU. Bulgaria, CM Crimea, CO Corsica. CR Central Russia, CT Crete, CZ Czechoslavakia. DE Denmark. EG Egypt. ER Eastern Russia, ET European Turkey, FI Finland, FR France. GE Germany, GR Greece. HO Holland. HU Hungary. ID Ireland. IR Iraq. IT Italy. JU Jugoslavia. LB Lebanon. LY Libya. MO Morocco. NO Norway. NR Northern Russia. PO Poland, PR Portugal, RO Romania. SA Sardinia, SD Sweden. SI Sicily. SP Spain, SW Switzerland, SY Syria, TR Anatolian Turkey. TU Tunisia, and WR Western Russia. Numbers representing species shown in Fig. I: (1) Echium atbieans, (2) E. anguslifolium\ (3) E. arenarium; (4) E. asperinum; (5) E. hoisserii, lusitanicum and ro.sutaium: (6) E. creticum: (7) E.fiavum; (8) E. humile\ (9) E. iiaticum\ (10) £.pan'iftora\ {[]) E. ptaniagineum,{\2) E. russicum,{]'i) E. sat'uticola;t]4) E. iubercutaium,andi]5) E. vutgare. have reached the limits of its potential distribu- migrating fronts from these points, and, finally, tion in Australia, as it has only spread very slowly amalgamation ofthe spreading fronts. Unlike E. into new areas over the past half century (Fig. 5a). italicum and E. vulgare, E. plantagineum has Those districts into which the plant has spread continued to increase its known distribution during this time invariably occur within the rapidly (15 districts year')- with many recent general pre-existing distribution of the species. In collections being made in areas previously devoid contrast, £. ptantagineum has been collected from of the plant, e.g.. Western Australia and the throughout Australia, except the very arid por- Northern Territory (Figs 4, 5). tions of Western Australia and latitudes < I6'S (Fig. 4). Although controversial (Kloot. 1982), the history of spread of E. plantigineum appears Australian eolleclions to have started as four or more isolated 'infes- Herbarium specimens of Echium increased at tation points' by 1900, with later movement as rates similar to numbers of districts occupied 356 F. Forcella. J. T. Wood and S. P. Dillon

Echium italicum I90I-I9I0 1931-1950 rx

V •

1911-1920 1951-1977

, -,...... V

1921-1930 rx X

Fig. 2 See Fig. 4 for details.

(Fig. 5). However, numbers of new collections per reached its 'final' distribution, e.g., E. vulgare decade (COL) was not correlated with numbers of from 1960-1977. new districts per decade (DIS) occupied, especially An index of collection intensity (INT) can be for the less common species. For example, regres- derived by dividing numbers of specimen collec- sion analyses of COL with DIS revealed R^ values of tions by numbers of districts occupied for any 002, 0 70 and 0 03 for E. italicum, E. plantagi- time period. By 1977 INT values were 3-1,4-7 and neum and E. vulgare, respectively. Lack of corre- 3 3 for £. italicum, E. planlagineum and E. spondence of COL with DIS stemmed from dispro- vulgare, respectively. Thus, INT was greater in portionate collection efforts after a species widespread species than in narrowly distributed Characteristics of invasive weeds 357

Echium vuigara

-1900 1941-1960 r

I... -1...

• • •

1901-1920 1961-1977

a / - f-^'j-

1921-1940

Fig. 3 Sec Fig. 4 for details.

Species. Furthermore, regressions of INT with DIS three species were 7-5, 3 9 and 3-4 mg seed ' revealed that INT increased with time for indi- (I.s.d.= l3 mg [/'<001]) for E. italicum, E. vidual species, with the rate of increase being 13 plantagineum and E. vutgare, respectively. Time and 1 2 times greater for E. ptantagineum than for to achieve more than 50% germination was less E. italicum and E. vulgare, respectively. for F. ptantagineum (1-2 days) than E. vulgare (3- 7 days) or E. italicum f'9-10 days). However, maximum germination percentage was lower for Germination the former than the latter species (65,75 and 85%, Experiment 1. Weights of viable seeds for the respectively), despite all seeds appearing to have 358 F. Forcella. J. T. Wood and S. P. Dillon

Echium ptantagintum

1831-1900 1941-1960

1901-1920 1961-1977

1921-1940

Figs 2-4 Spread of Echium italicum, E. vutgare and E. piantagineum, respectively, as represented by all herbarium specimens available in 1977 (Piggin, 1977). Each 1° by l'5° block represenls a mapping district in which at least one herbarium specimen was collected. fully developed embryos. lower temperatures nor ofE. vulgare at the lowest Germination rate index (Maguire, 1962), temperature. which integrates extent with speed of germination, was highest for E. plantagineum at each Experiment 2. From Day 1 to Day 14 the range of temperature regime (Table 1), with E. vulgare temperatures over which E. ptantagineum was intermediate and E. italieum lowest. Indices for able to germinate was about two and three times all species were greatest at the high temperature as great as that of E. vulgare and E. italieum, regime; no germination of E. itaiicum occurred at respectively (Fig. 6). At low temperatures (< 17'') Characteristics of invasive weeds 359

tions originating elsewhere (for E. planlagineum sec Ballard, 1970; Piggin, 1976; Trumble, 1937; for E. vulgare see Cross, 1931; Mitchell, 1926; no comparisons available for E. italicum).

Vegetative growth Leaf area. For E. plantagineum leaf area was correlated with temperature, but daylength did not affect this species (Fig. 7). Under each treatment, leaf area of E. ptantagineum was consistently and significantly (P<00!) greater 300 - than that ofthe other species. g 200- Leaf area of E. vulgare was not affected by daylength, but it was altered significantly by 100 temperature and the interaction of temperature and harvest date. Low temperature retarded leaf 1840 I860 1880 1900 1920 1940 I960 1980 area expansion; initially, high temperature pro- Time (years) moted it, but by the last two harvest dates leaf Fig. 5 Rales of spread (A) and rates of specimen collection (B) area at the intermediate temperature regime was of E. ilaticum (solid circle), E. vutgare (open circle) and E. equal to or greater than that at high temperature. planlagineum (square). Districts are 1 by I 5 ((. 115 km by F. vutgare commonly had the smallest leafarea of 136 km) as used by the Australian Grid Syslein. Dala derived from Piggin (1977), Fig. 5A adapted from Forcella & Harvey the three species. (1983). Long days, especially at high temperature, significantly promoted leaf area expansion of E. itatieum. Effects of temperature varied with time, Table I Germination rate index {sensu Maguirie, 1962), which but by the final harvest, leafarea was correlated integrates germination percentage and rate into a single value, with temperature (Fig, 7), Leafarea ofthis species forihree species of fi'cAiufn at three temperature regimes. Values wilh no superscripts in common differ significantly (/'<0 05). was considerably less than that of E. ptantagi- £. iialicum was nol included in the stalistical analysis neum. and usually equal to or greater than that of E. vutgare, except at low temperature. Tempera lure regime Results for leafarea were analysed on the basis of days after transplantation of 1- or 2-day-old species 28720° 23715-' 18 10 seedlings. If 'days after sowing' had been used, (rale index) differences would have been magnified for E. E. planlagineum 7'5'' 17" ptantagineum in comparison with other species, E. rutgari' 4.!'' 0 E. ilaticum 20 0 and reduced at high and increased at low temperature between E. italicum and E. vulgare. up to 45% of E. plantagineum seeds germinated, Shoot and root weights. Analyses of variance whereas only very few seeds of the other species revealed that both shoot and root dry weights did so. At higher temperatures both E. plantagi- generally responded to environmental conditions neum and F. vutgare germinated well, with E. in the same manner as leafarea. These traits will ptantagineum doing so significantly (/'<005) not, therefore, be elaborated further, except to more rapidly by Day 3 (Fig. 6). E. itaticum note that shoot:root ratios were consistently germinated well, albeit slowly, only within the greater in F. plantagineum (overall mean, 51) relatively narrow and high temperature band of than in either E. italicum {3-2) or E. vutgare (41). 33"-36^, where maximum germination was 26%. Thus, the relative response to temperature of these French seeds was similar to those from Flowering Australia {cf Experiment I). E. plantigineum produced flowers in eight of nine In both experiments germination behaviour of temperature/photoperiod combinations (Table our seed accessions was simitar to that of popula- 2). Flowering oecurred at progressively younger 360 F. Forcetla. J. T. Wood and S. P. Ditton

ages, to a minimum of 80 days, as daylength their seeds being transported to Australia. A increased and temperature decreased. Of the similar relationship has been observed for alien other species, only one plant of E. vulgare pro- thistles (Forcella & Wood, 1984) and clovers duced flowers in the environmental chambers (Morley & Katznelson, 1965) in Australia. Inter- (18710', 16 h). estingly, two countries, Albania and Yugoslavia, All E. italicum plants placed in a coidframe in which characterize native distributions of alien winter (July) and returned later to a heated thistles and clovers, are also associated with greenhouse (August) flowered within 30 days. native ranges of invasive species of Echium. Plants left in the coldframe produced flowers by Many species ot Echium unknown in Australia November. Plants placed directly in the green- may be distributed too narrowly in their native house without an intervening cold treatment did ranges to have had high probabilities of transport not flower. For E. vutgare, only plants remaining to other regions. However, some of these species, in coldframes throughout the winter produced namely F. parviflorum and E. russicum. have flowers in spring (November). biogeographie characteristics which somewhat resemble those of invasive Echium spp., implying that these plants may be potential alien weeds. Discussion Plant colonization in Australia, as determined from herbarium specimens, appears to have The alien herbaceous species of Echium in Austra- started with multiple infestation points {cf Kloot, lia all have very wide native distributions. This 1982). These points for Fehium were frequently trait, together with the presumed ornamental not near {i.e., within 1 ''fX-S'' latitude/longitude) of and/or medicinal values of each species (Bonnier, large cities and/or established herbaria. This 1912), may have increased the probabilities of implies that plant collectors neither favoured nor

- 60-

V. t 1

20- * ^' / • • QL -—f—:-•-:—

• (b) 1 t • • DoyI 60- • Day 2 * Day 3 : Day 7 :-Dcy 14 40-

/ /• —^

• - = ^- 1—t —t—: • . .

• (c)

10 15 20 25 30 35 Temperature (°C)

Fig. 6 Seed germinaiion percentage off. ;>/(7/7(flg/rti'i/m| A). E. r^/gur('(B)and £. ilaticum {C) o\er a range of constant lemperaturesand at five times after sowing. Each value is the mean of ihree replicates. Characteristics of invasive weeds 361 disfavoured rural or urban areas, and it alleviates other factors must have interacted with original some concern in using herbarium specimens as numbers of infestation points in determining data sources. ranges of the species in Australia. Potentially From multiple infestation points Fehium spp. adaptive ecological traits of these plants are spread as migrating fronts with varying degrees of discussed below. rapidity. For E. plantagineutn these migrating Numbers of herbarium specimens appear to be fronts coalesced into large ranges in which the useful for documenting the historical spread of a plant was more or less evenly distributed geo- species (Auld et at.. 1982/83: Lacey. 1957). but graphically. It was during the time of multiple tend to be inaeeuratc in determining whether a migrating fronts that this species spread exponen- species is still spreading. Numbers of occupied tially in its distribution. This suggests Ihat if a counties, districts or map grids ofsome kind must species spreads from only one or two infestation be employed to detect reeent movement of alien points, its rate of spread would be lower than if it weeds. was first introduced at several locations (Auld & Number of herbarium colleetions per unit area Coole, 1980), as seems to be true in the diiferen- appears to be a useful index of eollection inten- tial spread of Echium spp. (Figs 2-4). The greater sity, and perhaps commoness. at least within number of initial infestation points for E. ptanta- Echium. For example, collection intensity is I 4 gineum may have been due to its ornamental and 1-5 times greater for E. plantagineum than for value (K loot. 1982) and that its seeds are found in F. vutgare and E. itaticum. respectively. This a much wider variety of transported products eorresponds to recent findings that the most than the other species (Anon.. 1941, 1955, 1975: widespread animals are also the most loeally Low. 1969, 1978; Thomas et at.. 1984). abundant species (Hanski, 1981; Boek& Ricklefs. Relative to E. ptantagineum. distributions of £". 1983; Brown. 1983). itatieum and E. vutgare have stabilized. Thus Once an alien piant has been introduced il must

4 5 6 Time {weeks) 25715° -—-28720° Hg. 7 Increase of leaf areas under ihrec photnperiods and three lempcriilurc regimes for E. piantagineum (\),E. iiaiicum (B) «nd E. vutgare (C) as a funciion of lime after transplanting of I - und 2-day-old seedlings. Noie differing scales of leal area for each iilihe species. Six-week values ;il 12 hand \ii\i\ctv E.iuigareM 2.1 ,15 arc missing. All values represent means of four repliL-aies. 362 F. Forcetla. J. T. Wood and S. P. Ditton

Table 2 Age of F.chwm pianiagineum planls at iriitialion of value in interspecific competition has been noted anlhesis as aflected by nine cum hi na I ions of Icmperaturo and by Jennings & Aquino (1968), Hofstra & Stien- photiiperiod. Onh ii single plani flowered in ihe 2H 20 . 12 h Ireaimenl (240 days afier gcniim:iiu>nl. and no plarils Howered stra (1977) and Slatyer (1970). under N h at the same temperature. Leasi sijinilicanl iliHcrence Despite differenees in habit, a trait which is not (A'<0fl5) over all irealments is 25 days a reliable indicator of invasiveness (Foreella, 1985), all tested speeies of Echium were able to Tempeniiure regime flower and set seed within one year after seed Phoiopcriod 28 /20' 23 /15 18/10 germination in experimental settings. However, differences were pronounced in the degree of (hours) (diivs) environmental rcguhition of anthesis among the S X 201 179 12 >24(l IW 136 species. The highly invasive species flowered 16 11)1 100 m under nearly any temperature/photoperiod com- bination (Ballard & Grant Lipp, 1970). In contrast, the less common species required distinct vernalization and long photoperiods. require- respond to the physical environment in ways that ments which would constrain their distributions promote its survival. Survival will depend upon in Australia and elsewhere. physical hardiness and biological competitive- ness. Opportune seed germination, vigorous Some of our conclusions are apt to be ques- vegetative growth and prolific seed production, tioned, because analyses were based on seeds all under both stressful and benign physical derived from single populations. However, the conditions, would seem to be requisite traits. population genetics of the most important spe- How well are these traits reflected in the three eies, E. ptantagineum. justifies such narrow sam- differentially distributed species of Fehium in pling, at least for some analyses. For example. Australia? Wood & Degabriele (1985) have shown that The physical environment has eonsiderable attributable genetic variability is 3'5, 56 and 5-5 and differential clTeets on these Fehium species. times greater within populations than between The species which germinate over relatively nar- populations for relevant traits such as leaf area, row and somewhat high ranges of temperature, dry weight and age at flowering, respectively. and which germinate slowly, are restricted in Thus, the substantial genetic variability for these distribution. In contrast, F. ptantagineum seed traits within single populations may often encom- germination is rapid, like that of other wide- pass inter-population differenees. spread noxious weeds (Martin & Carnahan, 1983; For praetieal eharaeterization of an unknown Forcella. 1985), and it also occurs over a wide alien as either a potentially noxious weed or an range of temperatures. Responses of Eehium spp. innocuous waif, the range of its native distribu- are similar to differenees found in eommon and tion eoupled with the rapidity and extent of seed less common weeds of other genera (Cumming, germination appear to be the most useful traits 1959: Dillon & Forcella. 1984). Additionally, the examined in our studies. Thus speeies whose relatively high germination of £. ptantagineum at status as weeds are unknown, but which have temperatures between 10-20 would be favour- wide native ranges and whose seeds exhibit high able for establishment in Mediterranean-like en- germination rate indices are prime suspects as vironments, where soil temperatures in autumn potentially troublesome pests. Although sueh {when the growing season begins) are within this conclusions were derived from analyses of weeds range (Storrier. 1965). in Mediterranean Australia, other studies imply Vegetative growth of E. ptantigineum was that the principle may hold for weeds of different always greater than that of other species of regions (Cumming. 1959; Foreella, 1985; Foreeila Echium. It wasmonotonieally related to tempera- & Wood. 1984; Martin & Carnahan, 1983). Other tures, but otherwise unresponsive to temperature/ plant traits, such as ability to produce large leaf daylength combinations. Growth of less eommon areas quickly and propensity to flower under an species of Echium was regulated more rigorously array of environmental conditions, also charac- by environmental variables. High rates of leaf terize troublesome weeds. However, such traits area expansion under a variety of conditions could not be documented by plant quarantine would be important for an estabishing alien weed oflieials as easily as native distribution and germi- in competition with neighbouring plants. Its nation rate. Characteristics of invasive weeds 363

Ackno w ledgments FFTNRRUN-DOTHAN. N. (1978) Flora Pakiesiinti 3. Israel Aca- demy of Science and Humanity. Jerusalem. FoRCi-LLA. F. (I9K5) Final dislribution is related to rate of We thank R. Amor, J. Burdon, J. Carnahan, R. spread in alien weeds. Wved Research. 25, 181 191. Downes. A. M. Gill, R. H. Groves. P. Kioot, R. F()RCi[LLA. F. & HARvrY. S.J. (1983) Relative abundance in an Pullen and editorial staff of this journal for alien weed flora. Oecologia. 59, 292 295. FoRCLLLA. F. & W(KiD, J.T. (I9H4) ColonJzaiion potentials of helpful eomments on initial versions ofthis paper. alien weeds are relaled ID iheir native distributions: Implica- L. Wolf provided his mapping program. Staff of licns for plant quarantine. Journal of itie Australian tnsiiiuie the CSIRO Phytotron skillfully nurtured our I'f .•Igriculiural Science. 50, .15 4(). GIBBS. P.E. (1972) Echium. Flora Europeae 3 (eds T. G. Tutin ci plants on a daily basis. Data collection occurred at.), pp. 97-100. 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