This is a regular verb. It follows the conjugation pattern of the verb falar.
Present:
As flores murcham rápido no calor.
As flores murcham depressa com o calor.
The flowers wilt quickly in the heat.
Preterite:
A planta murchou ontem.
The plant wilted yesterday.
Imperfect:
As folhas murchavam no sol.
As folhas murchavam ao sol.
The leaves were wilting in the sun.