Plant of the week – 7th September – Cuckoo Pints: Arum maculatum and A. italicum

These are monocots, belonging to the family Araceae. Arum maculatum is native to Britain. Arum italicum has two subspecies, the subsp. neglectum is native, while subsp. italicum is a neophyte, recorded as being in cultivation by 1683 and occurring in the wild by 1905 (BRC, 2020). These species are similar in overall appearance, the most conspicuous differences being in the spotting and marbling of the leaves and colour of their veins. The species occasionally hybridise. A. maculatum has 2n=56 chromosomes, whereas A. italicum has 2n=84 chromosomes (Stace, 2019).

The photographs in this blog are of A. italicum subsp. italicum ‘Marmoratum’, taken in our garden, where it grows and is spreading.

Arum maculatum, being the predominant native species, has numerous English common names. Most of them gender-related, reflecting the flower structure’s resemblance to human genitalia (Lords and Ladies, Adam and Eve etc).

Several other species of the Araceae with similar flower structures have been introduced to the UK through the horticultural trade and have become established in the wild. These include Lysichiton americanus (skunk cabbage -introduced from North America, 1947), Calla palustris (bog arum – Europe, 1861), Zantedeschia aethiopica (altar lily -S. Africa 1952), Orontium aquaticum (golden club – North America 1990), Dracunculus vulgaris (dragon arum – Mediterranean 1918) and Arisarum proboscideum (mousetail plant – southern Europe 1872) (Stace and Crawley, 2015).

Tropical members of the Araceae include the popular house plant Monstera deliciosa (Swiss cheese plant). The spectacular flowering of the giant titan arum (Amorphopallus titanum – a species endemic to Sumatra) in glasshouses at the Royal Botanic Gardens Edinburgh attracts attention in the media each year https://www.rbge.org.uk/news/amorphophallus-titanum/.

Now incorporated in the Araceae are plants which were previously members of the Lemnaceae (duckweeds). While these small free-floating aquatic duckweeds appear very different to the arums, phylogenetic research places Lemna and its allies firmly in the Araceae (Cabrera et al., 2008), confirming suspicions raised 150 years ago by Engler (1876). It may seem surprising that duckweeds and arums are related, but they have a common ancestor in their evolutionary history. The structure of the inflorescence of duckweeds can be interpreted as a strongly reduced form of aroid inflorescence, with one or two male and female flowers sometimes subtended by a minute spathe. Within the current classification of the Araceae, the presence of numerous minute flowers packed onto a spadix and subtended or partly enclosed by a spathe is diagnostic for all genera within the Araceae, except for Lemna and its allies (Stace, 2019).

Cuckoo pints grow in woodlands and shady areas, and many of the horticultural introductions share a preference for shady, damp or aquatic habitats. The glossy green leaves appear in early Spring. The insignificant flowers are monoecious and protogynous (male and female flowers occur in the same inflorescence, but the female flowers mature before the males). The flowers appear after the leaves and are partly sunken on an unbranched inflorescence called a spadix which is half surrounded by a conspicuous spathe. The female flowers are at the bottom of the spadix and the male flowers form a ring above them. A sterile part of the spadix (sometimes called the appendix) protrudes into the open spathe. Whorls of sterile hairs separate the female from the male flowers, and the male flowers from the appendix (Lack and Diaz, 1991) and act as traps for pollinators.

The flowers are self-incompatible and are insect-pollinated, mainly by female owl-midges Psychoda phalaenoides L. (Lack and Diaz, 1991, Kite, 1996). The inflorescence produces an odour and is thermogenic. The odour of the spadix and its raised temperature attract the flies (bearing pollen from other flowers). According to Lack and Diaz (1991), Prime (1960) described the smell as ‘foul and urinous’. Lack and Diaz (1991) reported that spathes open in the morning and are immediately odiferous, but that most of the flies entered the spathe chamber later, after dark, having landed on the spathe and fallen into the trap. The flies are trapped in the chamber until the following day and their movement around the chamber transfers pollen from their bodies to receptive stigmas. The following day, pollen is shed by the male flowers, the trapping hairs shrivel and the flies escape, carrying new pollen to another flower. Kite (1996) found that the volatiles produced by the spadix include compounds which are also found in the volatiles of cow dung, on which the owl-midge breeds.

Bermadinger-Stabentheiner and Stabentheiner (1995) investigated thermogenesis in A. maculatum by infra-red thermography. On the first day of flowering, when the spathe was still firmly closed, the male flowers became thermogenic and reached surface temperatures of 4 – 8°C above ambient. As the spathe unfurled, the male flowers cooled, but the temperature of the sterile spathe rose to 5 – 14°C above ambient. Then, as the spathe cooled, the temperature of the male flowers rose again to 0.5 to 6.1°C above ambient and pollen grains were released. As the male flowers warmed, a ‘pleasant fruit-like scent’ was released, but this was overlain by a dung-like odour as the spathe warmed.

After flowering, the spathe and leaves wither, the lower part of the spadix extends and a conspicuous cluster of red berries appears in late summer from the fertilised female flowers.

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Cuckoo pints are geophytes which die down after fruiting and re-emerge in spring from an underground tuber. In autumn, a leaf bud develops on the tuber for the next season’s growth. Behind this are corms produced in previous years, bearing ring-like leaf scars and remains of roots. The strongly contractile roots pull the tubers to a depth of 20-30 cm below the surface (Sowter, 1949). According to Sowter, Scott & Sargant (1898) examined tubers which were 2 cm. below surface in May, and by October they were 7 cm. deep. Young tubers replanted near the surface regained their normal depth in a week.

Arum maculatum is widespread in Britain and Ireland, but in Scotland tends to occur mostly on the eastern coast. Sowter (1949) considered it to be naturalised and not indigenous north of the Firth of Forth and parts of Argyll, while the BRC suggests that it has been introduced in Northumberland and Cumbria and locations further north. The native A. italicum subsp. neglectum is mostly confined to southern England and the Channel Islands, whereas the neophyte subsp. italicum is scattered throughout Britain and Ireland.

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Toxicity
All parts of Arum maculatum are poisonous (Prakash Raju et al., 2018). The berries are extremely poisonous and contain oxalates of saponins which have needle-shaped crystals (raphides) which irritate the skin, mouth, tongue, and throat, and result in swelling of throat, difficulty breathing, burning pain, and an upset stomach. Fifty grams of the tuber can make you very seriously ill. The whole plant should be handled with care as it produces allergic reactions in some people. Reports also suggest similar toxicity of A. italicum.

Uses
On the Isle of Portland in Dorset, starch was extracted from the rhizomes and sold as a culinary thickening agent called ‘Portland sago’ or ‘Portland Arrowroot’, and it was used to starch ruffs in Elizabethan times. At one time it also had medicinal uses (Grieve, 1931) but these uses have been abandoned. The plants must have been very unpleasant to handle during the preparation of the starch and the methods of processing of it are not clear.

References
Bermadinger‐Stabentheiner, E and Stabentheiner, A 1995. Dynamics of thermogenesis and structure of epidermal tissues in inflorescences of Arum maculatum. New Phytologist, 131: 41-50. doi:10.1111/j.1469-8137.1995.tb03053.x

BRC Online Atlas of the British and Irish Flora https://www.brc.ac.uk/plantatlas/ maps downloaded 5^th September 2020

Cabrera, LI, Salazar, GA, Chase, MW, Mayo, SJ, Bogner, J and Dávila, P 2008. Phylogenetic relationships of aroids and duckweeds (Araceae) inferred from coding and noncoding plastid DNA. American Journal of Botany, 95: 1153-1165. doi:10.3732/ajb.0800073

Grieve, M 1931. A modern herbal. https://botanical.com/botanical/mgmh/mgmh.html

Kite, GC 1996. https://www.sciencedirect.com/science/article/pii/030519789500026Q

Lack, AJ and Diaz, A 1991. The pollination of Arum maculatum L. – a historical review and new observations. Watsonia 18: 333-342. http://archive.bsbi.org.uk/Wats18p333.pdf

Prakash Raju KNJ, Goel K, Anandhi D, Pandit VR, Surendar R, Sasikumar M. 2018. Wild tuber poisoning: Arum maculatum – A rare case report. Int J Crit Illn Inj Sci. 8(2):111-114. doi:10.4103/IJCIIS.IJCIIS_9_18

Prime, CT 1960. Lords and Ladies. New Naturalist Monograph M17, Collins, London.

Sowter, FA 1949. Arum maculatum L. Journal of Ecology, 37(1): 207-219.

Stace, CA and Crawley, MJ 2015. Alien Plants (Collins New Naturalist Library, Book 129) ISBN:978-0-00-750215-8

Stace, CA 2019. New Flora of the British Isles, Fourth edition. C&M Floristics. ISBN 978-1-5272-2630-2

Julia Wilson, photographs © Chris Jeffree