苏糖（英语：Threose，C₄H₈O₄）在分类上属于丁糖与醛糖，从费希尔式的角度看，中间两个碳原子上的羟基在碳骨架的两侧。

果聚糖： 菊粉 · 果聚糖β2→6

甘露聚糖

半乳聚糖

Threose is a four-carbon monosaccharide or carbohydrate with molecular formula C₄H₈O₄. It has a terminal aldehyde group rather than a ketone in its linear chain, and so is considered part of the aldose family of monosaccharides. The threose name can be used to refer to both the D- and L-stereoisomers, and more generally to the racemic mixture (D/L-, equal parts D- and L-) as well as to the more generic threose structure (absolute stereochemistry unspecified).