In an activity that I host I want to search for particular species and search hasn't worked properly for a while.
Today I searched for Tripleurospermum maritimum (using the search box above the map) and the records which came back included Aster tripolium, Triglochin maritima, Tripleurospermum inodorum, and Schistidium maritimum
If I use the search box below the map it works OK.
That top box is working as intended, it produces rough matches. There is a guide to using the explore pages that gives more detail, the relevant bit though is:
1. Top level filters
There are three filters at the top of the page that can be quickly and easily applied.
Search box
This can be used to search for any text in any part of any record. For instance, searching for the word "common" will produce records of Common Blue butterfly (and damselfy), records from sites such as Cotswold Commons, records with the word common in the comment boxes, etc. This provides a quick way of narrowing down the set of records, but is not very precise. To search for words in particular columns within the record grid you can specify a more precise search - for more information see the Help page on Using the Elasticsearch search box.
In theory you could just search for one species by putting it in speech marks, ie. "Tripleurospermum maritimum", however as you have discovered there is no need because you can search for single species by using the Elasticsearch box at the top of the records list (you could also do it using the create filter option).