Tasmanian Herbarium (HO) collections are shown to provide temporal and distributional data to monitor weed introductions into the State flora during the last 25 years. Information obtained from herbarium collections, the botanical literature, and anecdotal sources indicates that since 1970, 159 new plant taxa have been recorded as naturalised in Tasmania, bringing to a total over 740 weed species recorded from the State. Most of these species are from the families Poaceae (15.1%), Fabaceae (10.1%), Asteraceae (6.9%), Cyperaceae (5.7%), Rosaceae s.l. (5.0%), Caryophyllaceae and Liliaceae s.l. (3.8% each), Iridaceae (3.1%), and Juncaceae and Ranunculaceae (2.5% each). While for many taxa the mechanisms for introduction remain unknown, at least 35% were introduced as ornamentals, and some 5% arrived through agricultural practices. Of the 159 species, 19 are known only from Tasmania and have not been recorded from the Australian mainland. The majority of weeds are of European origin, with a high proportion being from Africa, North and South America, and mainland Australia, in that order. This study demonstrates that even with the current quarantine controls a large number of weed species have been introduced to the State flora in the last 25 years, and a considerable number of these species are recognised as potential environmental weeds. The number of new weed species recognised is also possibly due, in part, to more collections of weeds being undertaken in recent years. As a large percentage of the weeds identified are ornamentals, stricter controls on the introductions of new ornamentals may be needed. Some of the limitations of using herbarium collections to assess weed introductions are also discussed.
Of the 137 species of grass considered native to Tasmania, only eight use the C4 photosynthetic pathway. There are also approximately 137 grass species considered as introduced to Tasmania and 21% of these are C4. In total, there are 41 species from 20 genera of C4 grass recorded from Tasmania. Many of the introduced C4 species have a very limited distribution, however, and are generally confined to urban areas and along roadsides. Overall, Tasmania has fewer C4 grasses than would be expected from climate alone and few of the C4 grass species are widely distributed or abundant. However, the proportion of grasses recorded from Tasmania that use the C4 pathway has been increasing for the past century and is still increasing. General distribution and habitat notes are provided for all C4 grasses known to be native or naturalised in Tasmania.
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