The correct name for Satsuki is “Satsuki Tsutsuji”.  As the name suggests, Satsuki is a type of Tsutsuji (azalea), so Satsuki are very similar to Tsutsuji and difficult to distinguish them.  In the middle of the Edo period, many horticultural varieties were produced from Tsutsuji, which are endemic to Japan called Iwatsutsuji and Yamatsutsuji, and a boom in Tsutsuji cultivation occurred.  Around that time, in order to roughly distinguish between them, those that bloom from April to mid-May were called “Tsutsuji”, and those that bloom from late May to early June were called “Satsuki”.  The size of the flowers is 5 to 7 cm for Tsutsuji and 2 to 4 cm for Satsuki, and flowers bloom in chunks.  In addition, the flowers of Satsuki bloom first and the leaves come out after that, but Tsutsuji can be distinguished from the fact that the flowers bloom after the leaves come out.  The photo is Satsuki on the Asakayama Green Road in Sakai City, Osaka.

サツキの正しい呼び名は「サツキツツジ」。名前の示す通りツツジの一種なので、両者はよく似ていてなかなか見分けが付きません。江戸時代中期にイワツツジやヤマツツジと呼ばれる日本固有種のツツジから数多くの園芸品種が作り出され、ツツジ栽培のブームが起こりました。その頃に、これらをおおまかに区別するために、4月から5月中旬に開花するものを「ツツジ」、5月下旬から6月上旬に開花するものを「サツキ」と呼び分けるようになりました。花の大きさも、ツツジが５〜７cmに対し、サツキは２〜４cmとやや小さく、花が固まって咲きます。また、サツキは花が先に咲き、その後に葉が出てきますが、ツツジは葉が咲きに出た後に花が咲くことからも区別できます。写真は大阪堺市にある浅香山緑道のサツキです。