Source: Jane Reichhold at Aha Poetry has a lot of food for thought at the comparison. Some seem to write tanka if they overflow on syllable count for haiku but they are different beasts.
13 centuries———————–3 centuries
courtly —————————-merchants and lower class
literary—————————–part of a game
to savor beauty ——————–to open the heart
contemplation———————-quick and direct
emotional —————————aim to have no emotion
uses imagination——————–senses with concrete images
written to assigned themes ——-based on an experience
Tanka for the Memory by Jane Reichhold (same source)
From tanka’s long history – over 1300 years recorded in Japan- the most famous use of the poetry form of tanka was as secret messages between lovers. Arriving home in the morning, after having dallied with a lover all night, it became the custom of well-mannered persons to write an immediate thank-you note for the pleasures of the hospitality. Stylized into a convenient five lines of 5-7-5-7-7 onji, the little poem expressing one’s feelings were sent in special paper containers, written on a fan, or knotted on a branch or stem of a single blossom. These were delivered to the lover by personal messenger who then was given something to drink along with his chance to flirt with the household staff. During this interval a responding tanka was to be written in reply to the first note which the messanger would return to his master.