Complex sentence: On 9 January 1986 they returned to the location, collecting leaves and old flowers of what they thought was an undescribed species; however they were unable to collect fresh flowers or fruit because the species flowers only from April to June.
Split into simpler sentences: On 9 January 1986 they returned to the location, collecting leaves and old flowers of what they thought was an undescribed species. However they were unable to collect fresh flowers or fruit because the species flowers only from April to June.