Kamala Ekadashi is observed in Adhik Maas. In 2018, Kamala Ekadasi dates are: May 25 & June 10. These are also known as Padmini and Parama Ekadasi Vrat. Purushottam Ekadasi is another name for these Ekadasi vrat.
Kamala Ekadasi of May is also known as Padmini Ekadasi vrat. It falls in Shukla Paksha of Adhik Jyeshta Maas as per all Hindu lunar calendars..
Kamla Ekadasi of June 10 is also referred to as Parama Ekadasi vrata. It falls in Krishna Paksha of Adhik Jyeshta Month as per Marathi, Gujarati, Telugu & Kannada calendars. As per North Indian Hindi calendars also it falls in Adhik Jyeshta Month (Dwitiya Jyeshta Mahina).
Adhik Maasa Padmini Ekadasi (Kamla Ekadasi) Vrat katha is associated with Pulastya Muni and Kartaveeryarjuna (Sahasra Bahu / Sahasrarjuna). It is mentioned in the Skanda Purana as a conversation between Lord Sri Krishna and King Yudhishtira.