Sekizoku can be also classified into the following four types depending on the presence or absence of nakago (a stem; a projection area); the flat base type (without nakago), the concave base type (without nakago), the convex base type without nakago, the convex base type (with nakago).
更に、茎（なかご）の有無で分けると、全体を平基（無茎）式、凹基（無茎）式、凸基無茎式、凸基有茎式の4形式に分類することができる。