Hey Aspirant!

The process in which the margins of sepals and petals overlap without any specific direction it is known as  imbricate aestivation.

If this phenomenon does not occure in any particular direction as in Cassia and gulmohur, the aestivation is called imbricate. Aertivation might be of open, valvate, twisted or imbricate type. In imbricate aestivation there is an irregular overlapping of petals by one another, as mentioned earlier.

Thankyou!