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. ptantagi- neum 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 collec- tion 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