Aster novi-belgii L. s.l., Michaelmas-daisy

Account Summary

Growth form, preferred habitats and history of introduction

A. novi-belgii s.l. is comprised of a range of rhizomatous perennial herbs with erect stems up to 200 cm tall but generally less than that (including some truly dwarf forms), with clustered daisy-like flowerheads with ray florets that vary in colour from white to purplish-pink and bluish-purple arranged around a disc of yellow tubular florets. Since the plants flower from late August through until the frosts of November, they are called after the Christian church season of Michaelmas.

Michaelmas-daisies were early introductions to British gardens from North America in the 17th century and soon became established along roadsides, streamsides and eventually along railway embankments – all linked by being linear habitats (Ellis 1993; Stace & Crawley 2015). A. novi-belgii is believed to have been introduced to British gardens in 1710 and was first recorded beyond the garden gate by 1823. The seeds (or achenes, single-seeded dry fruits) have the typical attached parachute (or float) in the form of a pappus of hairs that facilitates spread by both wind and water. The efficiency of the dispersal process very possibly nowadays is chiefly associated with the slipstream of vehicles, at least in terrestrial situations.

Michaelmas-daisies are very commonly cultivated in gardens, but while they have spread very widely by self-sown seed (or been 'released' by deliberate dumping of excess garden material) into 'the wild' in Britain, there are comparatively few sites for them in Ireland. Reynolds (2002), however, lists rare records of seven taxa from sites scattered across the island. Common Michaelmas-daisy (A. novi-belgii × A. lanceolatus = A. × salignus Willd.) is a hybrid of garden origin which 'escapes' and becomes naturalised, often, but not always, in lakeshore and riverbank settings. It is by far the most common of the Michaelmas-daisy group, which overall can be difficult to identify since they involve hybridisation between three introduced American species. The second hybrid commonly recorded is Late Michaelmas-daisy (A. laeve × A. novi-belgii = A. × versicolor) and the third common species is Narrow-leaved Michaelmas-daisy (A. lanceolatus Willd.) (Ellis 1993). The other habitat where Michaelmas-daisies are most frequently recorded is on railway embankments, a situation where they very probably arise from discarded garden material and where subsequent seed dispersal is greatly facilitated by the slipstream effect generated by fast trains.

It is now known that the position is even more complex than Ellis (1993) describes it, since it is reckoned that at least seven American species of Aster are naturalised in B & I (Stace & Crawley 2015). In their catalogue of alien plants of the British Isles, Clement & Foster (1994) list 19 Michaelmas-daisy taxa that have been recorded in B & I, plus several other additional ones that have not been seen for many decades, which suggests that some of these forms may only be casuals.

Stace (2019), (who incidentally follows G.L. Nesom in transferring the Michaelmas-daisies to the genus Symphyotrichum Nees), says that, while, "These 2 hybrids [he is referring to S. × salignus and S. × versicolor (= A. × salignus and A. × versicolor)] and S. lanceolatum [= A. lanceolatus]) appear to be the commonest taxa, and show every grade of variation from 1 parent to the other. The N American spp. are numerous and very difficult; they have possibly given rise in cultivation in Britain to new taxa that add to the problems of identification."

Fermanagh occurrence

As the minutiae of the variation involved in local Michaelmas-daisies has not even begun to be investigated, it is essential to treat all of the Fermanagh records in the broad sense indicated above.

Michaelmas-daisies have been recorded in a total of ten Fermanagh tetrads. With the solitary exception of the first record listed above, they have all been confined to the shores of Upper Lough Erne and its islands. Furthermore, all but one of the Upper Lough records were made by members of the DOE(NI) habitat survey that concentrated on Upper Lough Erne during the 1986-7 period – the exception being a find made by RHN at Derryadd Marina on 14 September 1992. Regrettably, there are no voucher specimens for any of the records.

Threats

None.

References

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