Stephens said: "Mine is probably the most comprehensive collection of this genus to be found anywhere in the world. The purpose of the collection is for intellectual curiosity and pleasure."
Also new was Lachenalia held by Bill Squire in Dorset.
Last year Plant Heritage called for urgent action to safeguard the plight of heathers which, because of their loss of favour from gardeners in recent years, are at serious risk of being reduced to a handful of cultivars.
Following this, two new heather collections joined the scheme last year including Daboecia at Holehird Gardens, home of the Lakeland Horticultural Society and a collection of heathers at Nymans Garden in Haywards Heath that have a link to Sussex as a county.
Unusually, two new collections of water-loving plants joined the scheme including a collection of Caltha (water buttercups) and Water Irises both by Mark Haslett in Essex.
He has been working with the previous Caltha Collection holder John Carter of Rowden Gardens, Devon with the aim to rebuild the old Caltha collection.
He has plans to breed some new garden-worthy irises, while conserving the rarer ones and he is currently working on a propagation method to help boost the numbers on slower growing varieties.
Also joining the scheme was a collection of old double primroses Primula Vulgaris by Caroline Stone in Cornwall and a collection of Nepenthes (carnivorous pitcher plants) at Chester Zoo.Plant Heritage is the registered charity formerly known as the National Council for the Conservation of Plants and Gardens and holds 620 collections.
Conservation officer Sophie Leguil said: "The array of National Collections that we have had the pleasure to add to the Scheme in 2014 is a testament to the diversity of plants grown in the UK and Ireland.
"From public parks to private back gardens, Plant Heritage national collection holders are working relentlessly to conserve, propagate and research rare and unusual plants. On behalf of Plant Heritage, I would like to wish lots of success to our new collection holders."