Xanthosoma sagittifolium (Tannia, Cocoyam, Arrowhead Elephant Ear)

Potentially a better food source than Colocasia esculenta, Xanthosoma sagittifolium’s tubers/bulbs and young leaves are edible. The developing leaves are eaten once sufficiently cooked, and the underground stems are sometimes eaten once cooked and occasionally used to make flour. Although successful pollination is rare, these are popularly grown in the Pacific and South America as a common food staple.

Xanthosoma sagittifolium (Tannia, Yautia, Cocoyam, Arrowleaf Elephant Ear)
Deciduous: no
Hardiness Zones: 8-10
Height: 1.8-2.7 meters (6-9 feet) tall in the American tropics
Diameter: 0.6-1.2 meter (2-4 foot) spread
Growth Rate: moderately fast (to 1.2 meters (4 feet) tall and 1.2 meters (4 feet) wide in one year’s growth)
Age: perennial
Root System: tuberous, fairly extensive, fibrous
Subspecies: none

Tolerates: dappled shade
Problems (major): Leaf spots caused too much light are very detrimental. Snails, if not detected early, can inflict serious harm. Temperatures should consistently remain about 20 degrees Celsius, and tannia are intolerant of consistently soaked soil.
Problems (minor): Strong wind can harm these. Pythium rot, Rhizocotonia rot, and viruses are potential threats.
Poisonous: X. sagittifolium produces calcium oxalate crystals which irritate the mouth and throat if ingested.

Soil requirements: prefers rich, moist, well-drained soils (requires tall containers if not grown directly in the ground)
Air requirements: requires consistently warm and humid weather
Watering requirement: medium
Sun requirement: part-shade to full shade (preferred)

Leaf shape: Sagittate (shaped like an arrowhead), the petiole connects to the lamina, forming a “Y” “vein” structure. The petiole connects to the lamina at the very point/apex of the blade, where the blade splits from one sheet into two smaller sheets. The petioles can presumably either be a green or black color, depending on the plant.
Leaf size: The laminae/blades up to 4 feet long and 3 feet wide.
Stem: None, the petioles are “ribbed” and grow up to 3 feet tall
Flowering structure: inflorescence with a light-green peduncle, a green-yellow-white spathe (12-15 centimeters tall), and a yellowish-white spadix
Flowering frequency: blooms when amounts of daylight are changing (personally observed  in October and February)
Fruits: berry-like, uncommon
Subterranean storage organ: tuber, capable of breaking into multiple plants

Notable characteristics:
X. sagittifolium unfortunately has “extreme protogyny”, meaning that the female flowers are receptive for only a very short time. The foliage is attractive and edible for a short period of time. Under the right conditions, these can survive in shallow water.

Uses:
The tuberous/underground portion of Xanthosoma sagittifolium and Colocasia esculenta are both widely eaten in the Pacific. They contain a high concentration of carbohydrates and water, making them a food staple in certain regions. The younger leaves (moreso of X. sagittifolium than C. esculenta) can also be eaten if properly cooked and cleaned first.

Sources used:

Xanthosoma_sagittifolium_SIUC_1
The petiole attaches to the very end of the lamina, similar to some Alocasia

Xanthosoma_SIUC_2
Multiple X. sagittifolium leaves at the SIUC Life Science Greenhouse

Xan_sag_inflorescence_1
An inflorescence in early October
Xan_sag_inflorescence_2
An inflorescence in mid-February

The images provided were taken by me at the SIUC Life Science Greenhouse. They may be used, provided that this article/blog is appropriately cited  first.

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