AMORPHOPHALLUS KONJAC

Species

PROTOLOGUE:Amorphophallus konjac K.Koch, published in Wochenschrift für Gärtnerei und Pflanzenkunde 1.Jahrg. (1858).

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SYNONYMS:

HOMOTYPIC SYNONYMS: Amorphophallus rivierei var. konjac (K.Koch) Engl. in A.L.P.P.de Candolle & A.C.P.de Candolle, Monogr. Phan. 2: 313 (1879), nom. illeg. Brachyspatha konjac (K.Koch) K.Koch in Wochenschr. Gärtnerei Pflanzenk. 4: 13 (1858)

HETEROTYPIC SYNONYMS: Amorphophallus mairei H.Lév. in Repert. Spec. Nov. Regni Veg. 13: 259 (1914) Amorphophallus nanus H.Li & C.L.Long in Aroideana 11: 8 (1988 publ. 1989) Amorphophallus palmiformis Durieu ex Rivière in Actes Soc. Linn. Bordeaux 28: 15 (1869), not validly publ. Amorphophallus rivierei Durieu ex Carrière in Rev. Hort. (Paris) 42: 573 (1871) Conophallus konjak Schott in Syn. Aroid.: 34 (1856) Conophallus konniaku Schott ex Fesca in Beitr. Jap. Landwirthsch. 2(Spec. Theil): 241 (1893), orth. var. Hydrosme rivierei (Durieu ex Carrière) Engl. in Bot. Jahrb. Syst. 1: 188 (1880) Proteinophallus rivierei (Durieu ex Carrière) Hook.f. in Bot. Mag. 101: t. 6195 (1875) Tapeinophallus rivierei (Durieu ex Carrière) Baill. in Dict. Bot. 1(5): t. s.n. (1877)

OTHER NAMES: 花蘑芋 (huā móyù, Chinese); こんにゃく (konnyaku, Japanese — also the name of the flour and jelly made from the corm)

DISTRIBUTION: China (Yunnan): China South-Central.

DISTRIBUTION NOTE: Introduced into: China North-Central, China Southeast, East Himalaya, Korea, Nansei-shoto, Philippines, Thailand, Tibet, Vietnam Widely cultivated and often naturalised across East and Southeast Asia; a specimen found near Kota Kinabalu (Sabah, East Malaysia) by W. Mrazek may have been a weedy escape.⁴ iNaturalist: Chongqing, Guizhou, Hubei, Hunan, Sichuan, Yunnan.

SPECIES DESCRIPTION:

Tuber depressed globose, to ca. 30 cm in diam., to ca. 20 cm high, weighing to ca. 10 kg., brown, slightly glossy, seasonally producing numerous, long rhizomatous offsets with enlarged top part, these to ca. 50 cm long and ca. 3 cm in diam. Leaf solitary; petiole to ca. 100 cm long and ca. 8 cm in diam., smooth or with scattered punctiform warts at the base, background color dirty whitish pinkish, often nearly entirely covered by large, elongate, dark green confluent spots and smaller white dots; lamina highly dissected, diam. to ca. 200 cm; leaflets elliptic, acuminate, 3-10 cm long, ca. 2-6 cm in diam., upper side dull green.⁴

INFLORESCENCE:

Inflorescence solitary, long-peduncled; peduncle as petiole, to ca. 110 cm long, ca. 5 cm in diam.; spathe elliptic-lanceolate to broadly ovate-triangular, acute, ca. 10-60 cm long, ca. 10-55 cm in diam., base and limb more or less separated by a shallow constriction, outside base dirty pale brownish with blackish green spots, near the margin flushed with purple, inside base, basal part blackish purple and densely verrucate, verrucae tiny, punctiform, upper part whitish purplish, limb erect, undulate and/or longitudinally folded, margin spreading, outside dark purplish brown with scattered blackish green spots, inside uniformly dark brown, glossy. Spadix sessile, ca. 15-110 cm long.⁴

ECOLOGY:

Found in open situations or forest margins and thickets; altitude: to 3000 m⁴

PROPAGATION:

Cuttings of this species also proved difficult, with Juniper Level Botanic Garden's highest rooting percentages of 15.5% coming in early September. Even with proper timing, this was among the most difficult species to root.

ETYMOLOGY:

The epithet konjac preserves an early European rendering of an East Asian vernacular name, closely related to Japanese konnyaku. In Japan, konnyaku refers both to the plant and to the traditional gelatinous food produced from flour obtained from its tuber. The name is therefore unusual among Amorphophallus epithets in being rooted in the plant’s long history as a cultivated food crop rather than in a morphological character or a person’s name. The species has been cultivated and selected so extensively that the boundaries between its wild and cultivated morphology have become difficult to reconstruct.

NOTES:

1. Amorphophallus konjac is widely known in cultivation, both as an ornamental and as an economic crop. The latter especially in China and Japan. In Japan the tubers are used to produce Konnyaku, a type of flour used as the basis for many dietary products. Von Siebold brought the first specimens of this species to Western Europe from Japan ('Arisaema konjac'). As a result of extensive cultivation and selection, it has become obscure which part of the above described morphology is 'natural' and what is added through breeding/selection.⁴

2. The stench development in Amorphophallus konjac commences during three days and is already noticeable before the actual flowering starts. During female anthesis the appendix oozes out considerable amounts of a clear, slightly viscous fluid. This finally runs into the spathe base and leaks out through the basal opening. Amorphophallus konjac resembles Amorphophallus maxwellii but the latter has much longer styles, larger leaflets, a wider spathe, and a thinner appendix.⁴

3. A chromosome-level genome assembly of Amorphophallus konjac was published in 2022, giving the konjac industry its reference genome and identifying the gene families behind konjac glucomannan biosynthesis.⁸

4. Reports of outdoor culture of Amorphophallus konjac differ. In northwest Arkansas (nominally USDA zone 6), Steve Marak grew Amorphophallus konjac outdoors all year, giving the minimum temperature there as about −13 °F (−25 °C), and as about 14 °F (−10 °C) the year before he wrote; the plants seemed none the worse.¹⁵ In Somerset, England (European hardiness zone H5, 32 to 23 °F, or 0 to −5 °C), David Constantine found that Amorphophallus konjac survived outdoors, though he had not flowered it there.¹⁶ Victor Soukup, by contrast, wrote from a suburb of Cincinnati, Ohio (zone 6), that Amorphophallus konjac had not survived outdoors there several years earlier, and wondered whether his plants came from a much warmer growing region.¹⁷

5. Several growers reported Amorphophallus konjac overwintering outdoors in cold-winter American gardens. In Napoleon, Ohio (USDA zone 5), Clarence Waldron, who grew Amorphophallus konjac alongside Sauromatum venosum, found that some tubers missed at fall lifting, in an unprotected spot, emerged the next spring after winters of −10 °F or even lower, though he could not say how many others failed to survive and would not trust his large tubers to the elements.¹⁸ Victor Soukup reported that, of the Amorphophallus species considered hardy, only Amorphophallus konjac, supposedly the hardiest, would overwinter at Cincinnati, Ohio, with proper siting and winter protection as necessary.¹⁹ Steve Marak reported growing Amorphophallus konjac outdoors in zone 5/6 for years.²⁰

6. In northwest Arkansas (USDA zone 6), Steve Marak reported leaving Amorphophallus konjac in the ground year-round for about ten years, with overnight lows occasionally reaching about −13 °F (−25 °C).²¹ In a later message he gave winter lows of about −20 °F every five years or so, for short periods, and called Amorphophallus konjac one of the easiest Amorphophallus to grow and probably the hardiest.²² Plants left outdoors flowered less regularly than they had when he lifted them each fall, and in May rather than mid-March.²²

7. Steve Marak grew one clone of Amorphophallus konjac outdoors for more than 20 years in northwest Arkansas, USDA zone 6 with occasional zone 5 nights (zone 7 for the last seven or eight years). Plants he gave to Denver Botanic Gardens had come back there for some years. The other clones of Amorphophallus konjac that he acquired were less vigorous outdoors, and a couple disappeared.²³

8. In northwest Arkansas (USDA zone 6), where overnight lows once periodically reached −20 °F (−28 °C), Steve Marak found Amorphophallus konjac the only Amorphophallus that had proven itself through the worst the climate delivered.²⁴ His outdoor tubers of Amorphophallus konjac had been mostly left alone in two spots for more than 20 years, and plants he gave a friend at Denver Botanic Gardens had survived there for five or six years.²⁴,²⁵

STORY:

STORY TITLE: The vegetable that outgrew its genus

Amorphophallus konjac has been in the service of people for as long as almost any aroid on Earth. Its first documentation is in the Shen Nong Materia Medica of the Western Han Dynasty, and konjac glucomannan — the soluble fiber milled from its corm — has served Chinese medicine for over two thousand years, for purposes running from detoxification to tumor suppression to respiratory and skin disorders. In Japan the corm became food outright: boiled, ground and set with lime into konnyaku, the dense translucent jelly that anchors oden, is sliced thin as konnyaku sashimi, and, cut into noodles, becomes shirataki.

Botany met the vegetable late, and then could not decide what to call it. Philipp Franz von Siebold carried specimens from Japan to Europe under the garden name "Arisaema konjac"; Schott listed the plant as Conophallus konjak in 1856; and Karl Koch formally described Amorphophallus konjac in 1858 — Latinizing the Japanese kitchen word into a binomial — only to move it into yet another genus, Brachyspatha, in the same journal. Meanwhile French horticulture acquired the plant from Asia and named it all over again — Amorphophallus rivieri, published in the Revue Horticole of Paris in 1871. When Joseph Hooker figured that plant in Curtis's Botanical Magazine in 1875 — the Fitch chromolithograph shown below — he coined a fifth home for it, the genus Proteinophallus, and Engler shortly countered with a sixth combination in Hydrosme. Five genera in twenty-five years for one Japanese vegetable; the names all collapsed back into Amorphophallus konjac, and rivieri lingered on horticultural labels for a century.

Domestication muddied the picture as thoroughly as nomenclature did. The corm of a mature plant can reach thirty centimeters across and ten kilograms in weight, and after centuries of selection in China and Japan the monographers concede it has become obscure which parts of the plant's morphology are natural and which were added by breeding. The wild original is, in a real sense, no longer fully recoverable — the vegetable outgrew its own species description too.

The chemistry explains the career. Glucomannan makes up roughly half — 49 to 60 percent — of the corm's dry weight, alongside 10 to 30 percent starch, and it forms gels, films and coatings that hold their structure through cooking. That single polymer carried konjac from the apothecary to the kitchen to the materials laboratory: refined konjac flour entered Western markets as a food additive and dietary supplement, and modern konjac papers appear as often in food-hydrocolloid and biomaterials journals as in botany — konjac starch reviews, active food-packaging films, wound-dressing membranes.

In 2022 the species received a chromosome-level reference genome, built expressly to explain how those glucomannan chains are assembled; and as demand grows, related species such as Amorphophallus bulbifer and Amorphophallus albus are being evaluated as alternative konjac crops. Very few plants carry a two-thousand-year résumé that is still gaining pages.

CULTIVARS: