But news of the novelty, a couple of weeks before the start of Russia's watermelon season, has boosted the price in recent days to around $860, according to news reports.
That's more than 300 times the price of your standard melon, the Kyodo news agency said.
Japanese like to give watermelons as presents, especially during the summer gift-giving season known as ochugen.
Early in their development, the melons are put into transparent boxes, where they grow to maturity.
Why the cube? To save space in the small refrigerators found in the cramped quarters of most Japanese. Compared with Russia, the melons are a steal: about $80.
Before The Moscow Times carried an Interfax news agency report Friday on the strange fruit, they weren't leaping out of the bins.
"There has been no rush," an assistant said at one of the unidentified chain's stores. A few customers had bought them "just for fun."
Over the weekend, the price jumped about $150 as demand rose.
Not bad for something intended only as a decoration: The melons were picked for export to Russia before they were ripe, the BBC notes.
你见过方形的西瓜吗？日前，由日本培育的方形西瓜受到了俄罗斯富人的追捧。在莫斯科一家连锁商店内，每个方形西瓜的价格高达860美元（约合5300元人民币），是普通西瓜价格的300倍。
据《今日美国报》网站7月18日报道，方形西瓜是在日本培育的，最初只是为了方便存储，节省空间。它并不是转基因西瓜，只是人们在培育时，将其放在一个透明的盒子里，所以成熟时它就长成了方形。日本人喜欢把西瓜当做礼物送人。这些方形西瓜尚未成熟时就在日本摘下，销往俄罗斯。
方形西瓜与普通西瓜的味道相同，重量也差不多，大约每个6公斤，唯一不同的就是二者之间的价格。方形西瓜的价格已经迅速上涨到860美元左右，大约是普通西瓜的300倍。再过2周，俄罗斯自产的西瓜将在8月1日前后上架，普通西瓜的价格大约是每公斤15卢布（约为每斤1.4元人民币）
和俄罗斯相比，方形西瓜在原产地日本就很便宜，每个大约80美元（约合490元人民币）。
俄罗斯某连锁商店的销售助理表示，“西瓜热”并没有出现，有的顾客购买方形西瓜“只是为了好玩”。方形西瓜在俄罗斯最初售价700美元。不过，随着需求增加，价格一路飙升到860美元。
