ARUM ITALICUM
PROTOLOGUE: Arum italicum , published in The Gardeners Dictionary, ed. 8: no. 2 (1768). The protologue is reproduced below.
SYNONYMS:
HOMOTYPIC SYNONYMS: Arisarum italicum (Mill.) Raf.; Arum maculatum var. italicum (Mill.) O.Targ.Tozz.
DISTRIBUTION: Macaronesia, W. Europe to Iraq: Albania, Algeria, Armenia, Azerbaijan, Azores, Baleares, Bosnia and Herzegovina, Bulgaria, Canary Is., Corse, Croatia, Cyprus, France, Georgia-GE, Great Britain, Greece, Iraq, Italy, Kosovo, Kriti, Krym, Lebanon, Madeira, Montenegro, Morocco, North Caucasus, North Macedonia, Portugal, Sardegna, Serbia, Sicilia, Slovenia, Spain, Switzerland, Syria, Tunisia, Türkiye, Türkiye-in-Europe.
DISTRIBUTION NOTE: iNaturalist: Arezzo, Cremona, England, Gironde, Lisbon, Rome.
SPECIES DESCRIPTION:
Tuberous herb sprouting in early autumn or early winter from a rhizomatous tuber 3.5–7.5 cm long, 1.3–3 cm thick. Petiole terete to slightly D-shaped in cross-section, 15–35(–40) cm long, 5–9 (–12) mm wide, deep to mid-green, rarely dull purple. Leaf-blade narrowly or broadly hastate or sagittate-hastate or ovate-oblong, apex acute to obtuse, 9–35 (–40) cm long, 2–29 cm wide, plain deep green or with primary and main lateral veins slightly to heavily silver-grey, cream or yellowish green, more rarely blade marked with irregular black-purple spots or cloudy silver-grey blotches, or in various shades of green and white, or a combination of any of these.
INFLORESCENCE:
Inflorescence smelling strongly of stale urine or occasionally reminiscent of pineapple and citrus. Peduncle much shorter than the leaves, terete, 4.6–16 cm long, 6–11 mm wide, pale to mid-green, rarely dull purple. Spathe 11–27 (–38) cm long; spathe-tube oblong-ventricose, 3–5(–7) cm long, 1.5–2.5 (–3.5) cm wide, constricted apically, exterior pale to mid-green, sometimes stained brownish purple at the base and along the margins, interior greenish white, sometimes stained with purple apically, rarely entirely purple; spathe-limb elliptic-lanceolate to elliptic-ovate or broadly elliptic, 9–24.5(–31) cm long, 4–11 cm wide, erect, acute to acuminate, the tip drooping soon after opening, externally greenish white, occasionally flushed with brownish purple towards the margins and along the mid-vein, internally very pale green to almost white, sometimes stained with brownish purple along the margins, entire limb with a translucent quality. Spadix ¼–⅓ as long as the spathe-limb, 4.4–14 cm in total length; appendix clavate, long-stipitate, 3–10 cm long, 4–10 mm wide, pale to dark yellow or dull tawny brown, stipe sometimes pale. Staminodes in 2–5 whorls forming a zone 4–10 mm long; bristles filiform, flexuous, 3.5–5 mm long, cream; bases conical, ± verrucate. Interstices: upper 1.5–5 mm long, longitudinally ridged, sometimes obscurely so, pale cream, lower 0–3 mm long, with slight longitudinal ridging and some vestigial pistillode bases, cream. Staminate flowers in an oblong zone 3–6 mm long, 5–9.5 mm wide; anthers and connectives pale to mid-yellow. Pistillodes in 3 or 4 whorls, forming a zone 2.5–3 mm long; bristles filiform, flexuous, 3–5.5 mm long, cream basally, paler apically; bases conic to bulbiform, verrucate to smooth, pale to mid-yellow. Pistillate flowers in an oblong-cylindric cluster 9–14 mm long; ovaries ovoid-oblong, 2–3 mm long, pale green to off-white; stigma slightly darker. Fruiting spike oblong-cylindric, 5–9(–12) cm long, 2.5–3 cm wide; berries oblong-pyriform, 4–11 mm long, 3.5–5 mm wide.
ECOLOGY:
sea-level to 1,200 m; altitude: 0-1200 m
DISTRIBUTION MAPS:
ETYMOLOGY:
Of Italy.
NOTES:
1. Pollinated by midges, the chamber catch running to Chironomidae, Psychodidae, Ceratopogonidae and Drosophilidae — a broader suite than the near-single pollinator of Arum maculatum, and Psychoda phalaenoides, which pollinates that species, was not among 405 psychodids identified here.¹²
2. Boyce long separated a subspecies neglectum from subspecies italicum on leaf shape, principally the length and divergence of the basal lobes. After thirteen years of examining wild populations he concluded that the boundary does not hold and that both fall under Arum italicum subsp. italicum.¹³
3. The heat program has four phases and is run mostly by the male flowers, not the appendix: the male flowers warm on the day before the spathe opens, again on the opening day, and again on the day after pollination, while the appendix takes only the evening of the open day — its peak, 19.3 °C above ambient at about 21:30, is the largest of the four.¹²
4. Reproduction is expensive and mostly fails. Of 155 inflorescences followed through a season only 25 matured an infructescence; 77 aborted outright, and a further 46 were destroyed, three-quarters of those by herbivores eating the appendix. Every damaged inflorescence aborted, including ones that had already set fruit.¹⁴
5. Pollinator supply, not pollen quality, limits it: infructescence set tracked the mean number of Psychoda per inflorescence, which averaged only 1.7 ± 0.9 and fell through the season.¹⁴
6. Spontaneous selfing is impossible — 100 bagged inflorescences across five populations set no seed at all — but the barrier is timing, not incompatibility. Pollen moved by hand between inflorescences of one clone set as many fruits, as many seeds, and seeds as heavy as outcrossed pollen did.⁷
STORY:
STORY TITLE: The arithmetic of a trap
A trap is an expensive way to be pollinated, and Arum italicum keeps unusually detailed books. Marion Albre and Marc Gibernau followed 79 plants carrying 155 inflorescences through a single season on the Toulouse campus, visiting every two days from late March to mid-August, and recorded the fate of each one.
Twenty-five matured an infructescence. Seventy-seven aborted on their own. Thirty-four had the appendix eaten, five the spathe, seven were broken and seven rotted — and every damaged inflorescence aborted, including those that had already begun to set fruit. The season's yield was 16 percent.
The shortfall was not for want of insects. Almost every inflorescence caught something: only three of 174 held no flies at all. But the average haul was 1.7 midges, and it declined as the season went on. Infructescence set tracked that average closely, and tracked one species, Psychoda crassipenis, more closely still. The plants were not failing to attract; there were simply not enough loaded midges to go round.
Nor is the plant hedging by selfing. A hundred bagged inflorescences, across five populations in England and France, set not one seed between them. Yet the same pollen moved by hand from another inflorescence of the same clone set as many fruits, as many seeds, and seeds as heavy as pollen from ten meters away, and it germinated on the stigma just as readily. The block is dichogamy —male and female phases that never overlap within an inflorescence — and dichogamy cannot tell a clone-mate from a stranger. Arum italicum has no mechanism at all to avoid pollination by itself; it only has a mechanism that prevents an inflorescence from pollinating itself.
Set against Arum maculatum, which opens one smaller inflorescence and catches essentially one species of midge, Arum italicum is the high-volume strategy: 2.4 times the flowers, 4.6 times the seed, a broader suite of midges, and a tolerance for losing five inflorescences in six.
REFERENCES:
1. Plants of the World Online, Royal Botanic Gardens, Kew — Arum italicum
2. The Gardeners Dictionary, ed. 8: no. 2 (1768) — protologue.
4. Boyce, P.C. 1993. The Genus Arum: a Kew Magazine Monograph. Royal Botanic Gardens, Kew.
5. Boyce, P.C. 2006. Arum – a decade of change. Aroideana 29: 132–137.
13. Boyce, P.C. 2006. New observations on Arum italicum. The Plantsman, New Series 5(1): 36–39.
Additional photos by David Scherberich