Use the Wednesday Walk Index to search for plants seen on the various walks. Alternatively you can look up a list of walks and see which plants were found.
The page starts with two selection boxes - Location and Plant.
Select a location, and it shows a list of the plants seen at that location, for each visit. The table to the right of the plant names has a column for each visit date, and shows green for "plant seen" and grey for "not seen". The date at the head of the column is a link to the PDF for the walk at that location on that date.
Select a plant, and it shows a list of the walks on which that plant has been seen. Each walk has a list of the dates when the location was vistied - these are links to the PDF for the walk at that location on that date.