大约400种：在温带的亚洲，非洲和美国主要热带和亚热带，很少；中国有34种。
About 400 species: mostly tropical and subtropical, few in temperate Asia, Africa, and America; 34 species in China.
拉美国家产量通常很低，但科学研究已证明高产稳产在热带和亚热带地区已有可能。
In general, crop yields in Latin American countries are low but scientific research has demonstrated that high sustainable yields are possible in tropical and subtropical areas.
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