ARUM CRETICUM
PROTOLOGUE: Arum creticum , published in Diagnoses Plantarum Orientalium Novarum 13: 9 (1854). The protologue is reproduced below.
DISTRIBUTION: Kriti to SW. Türkiye: East Aegean Is., Kriti, Türkiye.
SPECIES DESCRIPTION:
Tuberous herb sprouting in early autumn from a discoid, vertically orientated tuber 4–6.5 cm across, 2–3 cm thick. Petiole 10–35 cm long, 4–7 mm wide, terete, bright mid-green, rarely dull purple for ± its whole length. Leaf-blade sagittate to oblong-sagittate, or oblong-sagittate-hastate, apex acute to obtuse, 8–27 cm long, 4–18.5 cm wide, bright mid-green.
INFLORESCENCE:
Inflorescence smelling strongly of freesia and lemon with a slightly sour overtone, reminiscent of naphtha at close quarters. Peduncle equal to or exceeding the leaves, terete, 12–30 cm long, 4–6 mm wide, bright mid-green, rarely deep purple. Spathe 4.5–24 cm long; spathe-tube goblet-shaped, 1.5–4 cm long, 1–3.5 cm wide, flaring apically, exterior pale to mid-yellow, with slight green staining at the base, interior pale yellow, generally paler than the exterior; spathe-limb lanceolate, 2.5–20 cm long, 1–5.5 cm wide, becoming reflexed and ± twisted at maturity, acuminate, externally and internally pale to mid-yellow, sometimes pale creamy white. Spadix equalling to just exceeding the spathe, 3.5–16.5 cm in total length; appendix fusiform-cylindric, laterally compressed, indistinctly stipitate, 2.5–11.5 cm long, 2–9 mm wide, deep to mid-yellow, stipe generally paler, appendix generally darker than the spathe-limb. Staminodes and pistillodes usually absent but occasionally small, subulate yellow staminodes and vestigial pistillodes may be present. Interstices: upper absent; lower 0–3.5 mm long, longitudinally ridged, pale yellow. Staminate flowers in a roughly conical zone 4–18 mm long, 2–4 mm wide, sometimes ± contiguous with the pistillate zone; anthers and connectives yellow. Pistillate flowers in a cylindric cluster 5–20 mm long, ovaries ovoid, 2–2.5 mm long, whitish green; stigma cream. Fruiting spike oblong-cylindric, 5–7 cm long, 2–2.5 cm wide; berries oblong, 5–11 mm long, 3–5 mm wide.
ECOLOGY:
Garrigue, rocky grassy hillsides, open meadows amongst low scrub; altitude: 250-1500 m
DISTRIBUTION MAPS:
ETYMOLOGY:
Of Kriti (Crete).
NOTES:
1. One of only two species in the genus pollinated by bees, chiefly Halictidae; mirid bugs and chrysomelid, melyrid and scarabaeid beetles are also recorded from the chamber but are probably not pollinators.¹⁰
2. The trap is half dismantled. Downward-pointing papillae are retained on the upper chamber and are broader than in any midge-pollinated species, so the bee is still made to slide into the chamber — but the lacunae between the cells are gone entirely, and so are the elongated sterile flowers that close the entrance in the rest of the genus.¹⁰
3. It is the one exception to an otherwise conserved genus-wide pattern: in every other species sampled the floral chamber headspace is more than 95 percent bicyclogermacrene, whatever the appendix happens to smell of.¹²
STORY:
STORY TITLE: The trap comes apart
Almost every Arum is a deceit trap. It offers nothing, smells of dung or carrion or fermenting fruit, and holds its pollinators overnight against their will on surfaces engineered to prevent escape: downward-pointing papillae that make the wall unclimbable, lacunae in the corners between the cells, and a palisade of elongated sterile flowers across the entrance, oiled so that insects slide off rather than climb.
Arum creticum does none of that. It smells sweet, it is visited in daylight by halictid bees, and it rewards them. It is also, with its sister Arum idaeum, the single exception to a pattern that otherwise holds right across the genus: in every other species sampled, whatever the appendix smells of, the air inside the floral chamber is more than 95 percent bicyclogermacrene. In these two it is not.
What makes the pair remarkable is that the machinery did not vanish at once. When Bröderbauer, Weber and Diaz put fifteen species under the scanning electron microscope, they found the trap coming apart in two steps. Arum creticum still has downward-pointing papillae, and they are broader than in any midge-pollinated species — the bee is still made to slide down into the chamber. But the lacunae are gone completely, and so are the elongated sterile flowers. Arum idaeum has gone further: no papillae anywhere, the spathe blade lined with plain tabular cells, no lacunae, no sterile flowers. Even the appendix, papillate in every other species examined, is smooth.
In the ordination of trap micro-anatomy the two bee species sit further from every other species than any other pair in the study. The trap that defines the genus is, in this corner of Crete, half dismantled in one species and gone in its sister.
REFERENCES:
1. Plants of the World Online, Royal Botanic Gardens, Kew — Arum creticum
2. Diagnoses Plantarum Orientalium Novarum 13: 9 (1854) — 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.
12. Gibernau, Macquart & Przetak 2004. Pollination in the genus Arum - a review. Aroideana 27: 148.
Additional photos by David Scherberich