According to most contemporary authors Typha is a nearly cosmopolitan genus of ca. 10-12 species. However, some authors (especially in countries belonging to the former USSR) apply a much narrower species concept (e.g. Krasnova 2011, Kapitonova & al. 2012, Mavrodiev & Kapitonova 2015). Two species are native in Belgium: Typha angustifolia L. and T. latifolia L. Their sterile hybrid (Typha xglauca Godr.) rarely occurs as well. In addition to these native species some others are increasingly cultivated as ornamentals for pond and lake margins (see Jäger et al. 2008 for an up-to-date account of the genus in cultivation in Central-Europe). Bernhardt & Gregor (2019) present a key for the identification of all taxa (incl. hybrids) that are offered for sale in the horticultural trade. Some of these species are rather reminiscent of both native species and might have been overlooked so far (especially Typha shuttleworthii W.D.J. Koch et Sond.; syn.: T. latifolia subsp. shuttleworthii (W.D.J. Koch et Sond.) Stoj. et Stef.). Fruits of Typha are easily wind-dispersed, often over long distances. Future occurrences of some of these ornamentals are therefore not unlikely.
Typha plants can be very vigorous and the genus is therefore sometimes considered invasive. However, invasive behavior is mostly seen in hybrid plants and these are apparently rare in Europe. In North America, on the contrary, invasive cattail hybrids are an increasing weed problem (Ciotir & al. 2017).
Female flowers in Typha are either subtended by (filiform) hairs or by hairs and scales (i.e. hairs that are conspicuously flattened and enlarged towards apex). This is an important character but not always easily assessed. It is preferably noticed at maturity when flowers readily detach.
The phylogenetic relationships within the genus Typha were recently studied by Kim & Choi (2011).
It was shown that commercially introduced Typha accessions (via the horticultural trade) can hide exotic lineages of native species, for instance for T. angustifolia and T. latifolia (Ciotir & Freeland 2016).
1 Female flowers subtended by hairs as well as scales (the latter, at least most of them, as wide as or wider than stigmas) === 2
1 Female flowers exclusively subtended by hairs or if scales are present these narrower than stigmas === 3
2 Leaves flat, more than 3 mm wide. Female part of inflorescence cylindrical, ca. 8-20(-35) cm long, never with a leaf-like bract. Stem 100-200 cm or longer, leafy (native) === Typha angustifolia
2 Leaves convex, up to 3 mm wide. Female part of inflorescence oblong-ovoid, rarely more than 5 cm long and often subtended by a leaf-like bract. Stem rarely exceeding 100 cm, leafless === T. minima
3 Female flowers subtended by hairs as well as scales. Sterile hybrids, often very tall (200 cm or more) === 4
3 Female flowers exclusively subtended by hairs. Fertile plants, rarely exceeding 200 cm === 5
4 Adaxial leaf surface and sheath with numerous mucilaginous (orangish) glands. Female spike at maturity pale brown === T. xprovincialis (T. domingensis x latifolia)
4 Mucilaginous glands absent from leaves and sheaths. Female spike medium to dark brown at maturity (native) === T. xglauca (T. angustifolia x latifolia)
5 Male and female part of inflorescence always distinctly separated (by 10-60 mm), the former at least twice as long as the latter. Leaves 2-4(-7) mm wide === T. laxmannii
5 Male and female part of inflorescence usually contiguous (more rarely separated by up to 25 mm), both parts about equal in length. Leaves 8-20 mm wide (native) === T. latifolia
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Literature
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