The arum plant of the genus Cyrtosperma is still almost unknown in Europe, but it is beautiful and very easy to care for. They are swamp plants that grow in the seasonal waterlogged forests of Papua New Guinea, Indonesia and surrounding islands. They even tolerate brackish water.
They have an erect habit with vertical leaves, similar to some Alocasia. They always grow large, with a height of 2 to 4 meters. The leaves are pointed and arrow-shaped. They form very thick rhizomes, which can also be more than 2 m long and are eaten cooked in their homeland. Old rhizomes can weigh more than 100 kg! This makes it the largest vegetable in the world.
The plants on offer here may include the species C. giganteum, a very rare species that is only found a few times in nature. It was first collected in 1907 by the Dutch botanist Gerard Martinus Versteeg and in 1909 by also the Dutch doctor and psychiatrist Lucien Albert Marie von Römer. Based on Versteeg’s collection, Adolf Engler named the plant Cyrtosperma giganteum. There was no further scientific record of this species for more than 90 years (!) until it was rediscovered in 1999 and 2000 on two expeditions in southern Papua. However, encounters with this plant were not published, except for one photo used to describe the genus Cyrtosperma in Plants of the World Online. This species was only rediscovered in December 2020 and this time also scientifically researched (link to the paper) First they were identified as the commonly cultivated C. merkusii. As they grew and it became clear that something else was involved, they were later identified as Cyrtosperma sp. “Papua” and finally (temporarily) identified as C. giganteum.
However, this plant shows some striking differences in the description of C. giganteum that very little is known about. The petiole is significantly shorter and the wavy leaves are very irregular. So whether it really is C. giganteum remains unclear. It is very easy to care for them if you keep them in a pond. This swamp plant is best grown in a tall pot, which is about halfway submerged in water. They grow best in mesh baskets for pond plants. Normal potting soil or peat or peat substitutes such as coconut husk are suitable as substrates. They like it warm, they do best at temperatures above 22 °C. When the temperature is above 15°C at night, they can also be placed outside for better growth. Be sure to bring them back in early fall as they are quite sensitive to cold temperatures. They should be in full to bright sun, but must first get used to direct sunlight after winter. You must fertilize abundantly. It is best to add the fertilizer solution directly to the water they are in and replace it once a week.
Translated, Engler’s Latin description reads: “Leaf with petiole to 2.5 m long, adult blade coriaceous, ovate-sagittate, anterior lobe to about 75 cm long, 70 cm wide at the base, obtuse or apiculate at the apex, posterior lobes to 1 m or more long, 50 cm wide, bent back, subacute, separated by a deep acute sinus, with about 8 distant lateral primary nerves joined into a marginal collective vein, posterior costae naked in the sinus for about 10 cm. Peduncle to 4.5 cm diam., smooth. Spathe ovate-lanceolate bearing a long acumen, reddish-brown, convolute below, c. 8 cm diam., c. 35 cm or more long; spadix dark rose, stipitate for 2 cm, 21 cm long, about 4 cm thick. Stamens 4-5, filaments to 1 mm long. Pistil 4 mm long, ovary pluriovulate. Perianth with 4-5 tepals 3.5 mm long. Fruiting spadix to 36 cm long, 9 cm thick. Berries ellipsoid, green, 1.5 cm long, 6 mm thick. Seeds several.”
Diagnostic Ovary multiovulate; fruit up to 5-seeded; infructescence massive, to c. 35 cm long and c. 11 cm thick. Lorentz river in Irian Jaya. Distribution Irian Jaya; known only from three collections from Lorentz (Noord) River.