Arum italicum Mill. (S- and SW-Eur., W-As., N-Afr., Macaronesia) – An increasingly naturalised garden escape or -throw-out. Usually found in woodland, shrubberies, hedgerows,… on damp, nitrophilous substratum. Habitats are quite often strongly influenced by man (plantations, places where garden waste is discarded,…). Arum italicum appears to be more widely distributed in the western portion of Belgium (see Vanhecke 2006). In this area it grows rather close to its native area in the British Isles and native status has been claimed, at least for subsp. neglectum (F. Townsend) Prime (syn.: Arum neglectum (F. Townsend) Ridley). Taken into account the artificial character of most of its locations, its relatively recent discovery in Belgium (apparently unknown before 1955) and the absence of a clear-cut distribution area in Belgium, native status of Arum italicum seems to be very unlikely (Verloove 2002, 2006, Vanhecke 2006).
Arum italicum is fast spreading in some regions and sometimes considered an invasive species, for instance in New York (Atha & al. 2017).
Several taxa have been distinguished within Arum italicum. In Belgium at least subsp. italicum and subsp. neglectum have been recorded. Typical plants of both are well differentiated but more or less intermediate populations do exist. Boyce (2006) recently confirmed that the boundaries are blurred and the previous distinctions not significant. The extremes of both subspecies are characterised as follows:
- Leaves with conspicuous whitish veins, never dark-spotted. Lateral leaf lobes divergent, never overlapping. Fruit with 2-4 seeds === subsp. italicum
- Leaves with veins slightly paler than rest of leaf, sometimes dark-spotted. Lateral leaf lobes slightly convergent, often overlapping. Fruit with 1-2 seeds === subsp. neglectum
An up-to-date overview of the cultivars of Arum italicum is presented by Rice (2010). Things are further complicated by the existence of hybrids between native Arum maculatum and A. italicum (Stace 2010). These plants much resemble Arum italicum subsp. neglectum in having dark-spotted leaves appearing in autumn but are probably fully sterile. To our knowledge, such hybrids have not been reported from Belgium so far but, since both taxa are increasingly often found together, they are likely to be produced.
Arum maculatum is a common native species in large parts of Belgium (less so in the northern and northwestern portion). It is however frequently cultivated and at least part of the Belgian populations are in fact of garden-origin.
A very closely related species from east-central Europe, Arum orientale Bieb., is also cultivated and might have been overlooked. It was recently claimed from an old estate in Rummen (Warandebos) but this needs confirmation. Arum orientale is distinguished from A. maculatum in having unspotted leaves and vertical tubers (always horizontal in the latter).
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Selected literature:
Atha D., Boom B., Thornbrough A., Kurtz J., McIntyre L., Hagen M., Schuler J.A., Rohleder L., Hewitt S.J. & Kelly J. (2017) Arum italicum (Araceae) is invasive in New York. Phytoneuron 2017-31: 1–18. [available online at: http://www.phytoneuron.net/2017Phytoneuron/31PhytoN-ArumitalicumNYBG.pdf]
Boyce P. (2006) New observations on Arum italicum. The Plantsman N.S. 5(1): 36-39.
Rice G. (2010) Arum italicum and its cultivars. The Plantsman N.S. 9(4): 212-217.
Stace C. (2010) New flora of the British Isles, 3th ed.: XXXII + 1232 p. Cambridge University Press.
Vanhecke L. (2006) Arum italicum. In: Van Landuyt W., Hoste I., Vanhecke L., Van den Bremt P., Vercruysse W. & De Beer D., Atlas van de Flora van Vlaanderen en het Brussels Gewest. Instituut voor natuur- en bosonderzoek, Nationale Plantentuin van België en Flo.Wer: 163.
Verloove F. (2002) Ingeburgerde plantensoorten in Vlaanderen. Mededeling van het Instituut voor Natuurbehoud n° 20: 227 p.
Verloove F. (2006) Catalogue of neophytes in Belgium. Scripta Botanica Belgica 39: 89 p.