This summer the RCP garden celebrated the life and work of William Shakespeare with a garden trail and accompanying leaflet highlighting plants growing here that appear in his poetry. A series of 33 gold-coloured labels have been engraved with these verses and placed beside the relevant plants, one of which is Senna. 

The lines refer to the plant’s medicinal properties and use as a laxative, and come towards the end of the play. Macbeth’s murderous career is coming to its violent end and the armies of his enemies are advancing. Lady Macbeth has descended into guilt-ridden madness and the doctor called to attend her has a conversation with a defiant Macbeth who still believes in his invincibility. 

(Dunsinane. A room in the castle)

Macbeth: Throw physic to the dogs; I'll none of it. 
Come, put mine armour on; give me my staff. 
Seyton, send out. Doctor, the thanes fly from me. 
Come, sir, dispatch. If thou couldst, doctor, cast 
The water of my land, find her disease, 
And purge it to a sound and pristine health, 
I would applaud thee to the very echo, 
That should applaud again.—Pull't off, I say.— 
What rhubarb, senna, or what purgative drug, 
Would scour these English hence? Hear'st thou of them? 

Doctor: Ay, my good lord; your royal preparation 
Makes us hear something. 

Macbeth: Bring it after me. 
I will not be afraid of death and bane, 
Till Birnam forest come to Dunsinane. 

Doctor: [Aside] Were I from Dunsinane away and clear, 
Profit again should hardly draw me here. 

Macbeth, act 5, scene 3

This beautiful legume is currently blooming now in the Garden of Medicinal Plants, in bed O. The plant originates from the South American countries of Brazil, Argentina and Uruguay. It’s the source of the herbal medicine senekot; every part of the plant contains anthraquinones which, if taken internally, act as a powerful laxative to treat constipation. When used regularly, the nerves to the large bowel may be destroyed, leaving a permanently dilated large bowel that never functions properly again.

Sam Crosfield, assistant gardener

• Over 1,000 species grow in the RCP Garden of Medicinal Plants: find out more in the plant database. The garden is open daily and tours are available.