Tulsi – that can be used in the service of Radha and Krishna (like deity worship) is commonly found in two varieties – the green coloured Lakshmi Tulsi (or Radha Tulsi) and the purple hued Krishna Tulsi (also Shyam Tulsi, Vishnu Tulsi or Vishnu Priya Tulsi). Ayurveda also uses names like White Tulsi (Shweta Tulsi) and Black Tulsi (Krushna Tulsi) respectively.
Both kinds are considered holy and therefore the Latin name for both is Ocimum Sanctum.
They are very similar plants – but you can also discriminate between them. The mentioned purple hued leaves of the Krishna Tulsi (Shyam Tulsi) are only visible by good strong sunlight over the year, otherwise the leaves will also stay green. But the color of the blossoms are always more purple than that of the Radha Tulsi.
Other Herbs are also named Tulsi, like Clove Tulsi (that’s the Ram Tulsi, gets very big – like 3 meters in hot climate, Latin name: ocimum gratissimum) Van Tulsi – that’s actually Oregano and wild forms of it grow even in the Himalayas and cold German forest.
There are probably more Plants that can come by the name Tulsi, but only the first two – Laxmi Tulsi and Krishna Tulsi (Ocimum Sanctum) are considered to be holy and have to be used in the worship (puja) of the Gaudiya Vaishnavas (not the Ram Tulsi).
I was told that the Ram Tulsi (Ocimum Gratissimum) is used in the Sri Sampradaya but I don’t have any personal experience with that and I highly doubt it.
But Ram Tulsi is sometimes used for making (bigger) Murtis (amulets) for malas, wooden necklace or even Japa Malas (perhaps) because the stock of a Ram Tulsi tree can become very big.
In the western Vaishnava community I have seen that devotees use Ram Tulsi also and I have found also confusion about the topic, so this little information may help I hope. Any questions or comments are appreciated.