ARUM PICTUM
PROTOLOGUE: Arum pictum , published in Supplementum Plantarum: 410 (1782). The protologue is reproduced below.
SYNONYMS:
HOMOTYPIC SYNONYMS: Arisarum pictum (L.f.) Raf.; Gymnomesium pictum (L.f.) Schott
HETEROTYPIC SYNONYMS: Arum balearicum Buc'hoz; Arum corsicum Loisel.; Arum pictum lusus bispathaceum Engl.; Arum pictum subsp. sagittifolium Rosselló & L.Sáez
DISTRIBUTION: Baleares to W. Italy: Baleares, Corse, Italy, Sardegna.
DISTRIBUTION NOTE: iNaturalist: Cagliari, Carbonia-Iglesias, Grosseto, Medio Campidano, Nuoro, Ogliastra, Olbia-Tempio, Oristano, Sassari.
SPECIES DESCRIPTION:
Tuberous herb sprouting in early to mid-autumn from a discoid vertical tuber 5–7 cm across, 2–2.5 cm thick. Petiole semiterete, 15–25 cm long, 2–12 mm wide, pale to mid-green with slight purple staining basally, with a conspicuous, open, triangular basal sheath. Leaf-blade ovate-cordate, apex acute to obtuse, 9–25 cm long, 6–18 cm wide, shiny, deep metallic green tinged with purple, especially along the margins when first expanded, the veins paler, blade later becoming dull, deep green with a purple tinge and creamy white to silvery grey main and lateral veins, leaves very occasionally plain green.
INFLORESCENCE:
Inflorescence appearing before or with the leaves, smelling strongly of horse-dung. Peduncle sessile at ground level, or rarely with up to 2 cm visible if growing in deep shade, terete, pale green. Spathe 11.5–21.5 cm long; spathe-tube oblong-cylindric, 2.5–5.5 cm long, 2.5–3 cm wide, constricted at the apex, exterior off-white below ground, pale green with purple staining above ground, interior dirty white with scattered purple spots and staining along the margins; spathe-limb elliptic, 9–16 cm long, 4–6.5 (–8) cm wide, slightly cucullate, shortly acuminate, externally mid-green with heavy, deep purple staining, especially along the margins at the apex, internally velvety deep purple, the apex occasionally mottled mid-green. Spadix approximately ⅗ as long as spathe-limb, 8–13 cm in total length; appendix stoutly clavate, cylindric, long-stipitate, 6–11 cm long, 7–15 mm wide, deep purple-black with a satin sheen. Staminodes in 3 whorls forming a zone 3–5 mm long; bristles subulate, stiff, 3–4.5 mm long, cream; bases slightly swollen, smooth, cream. Interstices: upper 2–3 mm long, longitudinally ridged, off-white; lower 1–2 mm long, longitudinally deeply sulcate, cream. Staminate flowers in an oblong to globose zone 5–7 mm long and wide; anthers pale cream and connectives off-white. Pistillodes absent or very rarely a few vestigial bases present above the pistillate flowers. Pistillate flowers in a globose-cylindric cluster 11–13 cm long, 10–11 mm wide; ovaries oblong, tapering basally, 2.5–3 mm long, pale cream; stigma yellow. Fruiting spike elongate-globose, 2.5–5 cm long, 2–4 cm wide; berries oblong-globose, 5–11 mm long, 5–7 mm wide.
ECOLOGY:
In garrigue and Pinus halepensis maquis; altitude: 0-500 m
DISTRIBUTION MAPS:
ETYMOLOGY:
Latin pictus, “painted”, for the leaf, whose main and lateral veins develop as a creamy white to silvery grey network.
NOTES:
1. Alone in the genus it flowers in autumn, in October, rather than in spring.⁴
2. Its appendix is dark purple rather than the yellow of Arum italicum, its carpels greenish rather than whitish, and the zone of sterile flowers narrower.⁴
STORY:
STORY TITLE: October, in the Pisa botanical garden
Every other Arum flowers in spring. Arum pictum flowers in October, on Corsica, Sardinia, the Balearics and a corner of Tuscany, and it was that oddity that put it in front of Giovanni Arcangeli in the autumn of 1886.
Arcangeli had a single inflorescence in the botanical garden at Pisa. Before opening it he made a prediction from its structure alone: the chamber, he reasoned, was eminently suited to imprison Diptera rather than Coleoptera, and its lurid red spathe suggested its visitors would differ from those of Arum italicum. He noted that on picking it gave off an odor like decomposing fruit.
Then he killed the entire contents with benzine and sent the catch to three entomologists. Ninety-five insects: ninety of them flies, and eighty-six of those a single species of lesser dung fly, Borborus equinus. The remainder were four more dung flies, three Aphodius beetles, one rove beetle, and one small wasp — almost certainly a parasitoid, present to lay its eggs in the bodies of the flies rather than to visit the plant at all.
The prediction held. What is striking at this distance is Arcangeli's refusal to overclaim on the strength of it. One inflorescence, in cultivation, could not establish which insects pollinate the species; it deserved consideration only as a first observation. He also recorded the characters that separate it from Arum italicum — a dark purple appendix rather than a yellow one, greenish carpels rather than whitish, a narrower band of sterile flowers — and left the pollination question open for someone with a population and a season.
REFERENCES:
1. Plants of the World Online, Royal Botanic Gardens, Kew — Arum pictum
2. Supplementum Plantarum: 410 (1782) — 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.
Additional photos by David Scherberich