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| Colocasia spongifolia P.J.Matthews, V.D.Nguyen, Q.Fang & C.L.Long, in Matthews, Nguyen, Fang & Long, 2022. |
Abstract
Colocasia spongifolia sp. nov. (Araceae) is a large herb in forest edges on mountain slopes in southern China and central Vietnam. The plant is remarkable for its distinct vegetative morphology, while floral morphology places it as a close wild relative of C. esculenta (taro), among other closely-related species. The name given here reflects a thick, rubbery, spongy leaf blade unlike the blades in other Colocasia species known to us. The blade has exceptionally large spongy mesophyll cavities that are visible to the naked eye. Vegetative reproduction appears to be limited to direct (though shy) sprouting of lateral buds to form new erect stems, without production of side-tubers or stolons. In contrast to other Colocasia species, dense spreading colonies (clumps or patches) were not seen.
Keywords: Aroideae, new species, substomatal cavity, marginal vein, peduncle, staminodes, fruit
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| Habit and habitat of Colocasia spongifolia. A. Single plant ca. 1 m tall, on road bank, at 962 m elevation. B. Scatter of adult plants (arrow heads) in upper area of a recent slip face, above road, at 676 m. C. Plants collected from roadside at 854 m; blades pale, milky-green on underside. D. Same site as B, with young seedling emerging from a bed of moss and liverwort. Photos: Peter J. Matthews. |
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| Floral habit and structure of Colocasia spongifolia. A. Type specimen in situ with open, spathe limb (apex is reflexed out of view), and green spathe tube (ca. 6 cm long). B. Adjacent plant with inflorescences and prophylls. C. Spadix showing from top: sterile appendix, staminate (male) zone, sterile interstice, and green pistillate (female) zone with tapered, conical form. D. Detail of female zone showing a few basal staminodes. E–G. Berries of the preserved type specimen. G. Dissected berry with orthotropous ovules (some outlined) attached by funicles to parietal placentae (arrows). H. Surface of male zone showing closely-packed synandria. I. Synandria separated to show fused anther sacs beneath apical pores (example in center has 8 pores, 8 anthers) J. Mature fruiting head, with single berry removed to show seed packing and 67 seeds extracted (scale bar units: 1 mm) (Bach Ma NP; type 2020; fruit and seeds 2018). Photos: Nguyen Van Du and Peter J. Matthews. |
Colocasia spongifolia P.J.Matthews, V.D.Nguyen, Q.Fang & C.L.Long, sp. nov.
In contrast to Colocasia esculenta, C. formosana, C. gongii and other species, C. spongifolia has a thick, rubbery leaf blade with smooth underside (vs thin, not-rubbery, with raised interprimary veins on underside). It differs from C. esculenta, C. formosana, C. lihengiae and other species by having a stem without side-tubers or stolons (vs with side-tubers or stolons) and staminodes absent or rare at base of female zone (vs many or abundant throughout the male zone). It differs from C. lihengeae, C. yunnanensis, and some cultivars of C. esculenta by having a sterile appendix (vs much reduced or absent).
Etymology:—The specific epithet is derived from the distinct character of the leaf blade (visibly spongy appearance and rubbery to touch).
Ecology:—In contrast to other Colocasia species, dense spreading colonies (clumps or patches) were not seen. The persistent adaxial buds of C. spongifolia may support regeneration from fallen, decumbent stems. During ex situ cultivation, it has been possible to force buds to sprout by removing the stem apex and placing the stem horizontally on damp soil. At Bach Ma, immature fruiting heads were marked by the teeth of an unknown terrestrial frugivore (possibly a seed disperser, and likely a small mammal), and living larvae of a specialist pollinator (Colocasiomyia sp.) were found between berries on mature fruiting heads.
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| Blades of Colocasia spongifolia. A. Sub-marginal and marginal collective veins, with laminal tissue (2–4 mm) between. B. Marginal collective veins fused below shallow sinus. C. Underside with spongy appearance produced by “false pores”; and thick, rubbery texture indicated by axial wrinkles formed in crease. D. Underside showing primary vein and pinnate lateral veins surrounded by spongy tissue. E. Sub-stomatal cavities revealed by transmitted light (scale unit 0.25 mm), F. Sub-stomatal cavities revealed by removing lower epidermis (A–D: Mengla County, 2018. E–F: Bach Ma NP seedling, ex situ). Photos: Peter J. Matthews. |
Peter J. Matthews, Van Du Nguyen, Qiong Fang and Chun-Lin Long. 2022. Colocasia spongifolia sp. nov. (Araceae) in southern China and central Vietnam. Phytotaxa. 541(1); 1-9. DOI: 10.11646/phytotaxa.541.1.1
