Dactylis - Ornamental grass suited for perennial border. A good variegared Dactylis is Dactyla glomerata Variegata.
Dactylorhyza - Marsh Orchid - Now you can have your own outdoor orchids - especially in a woodland or meadow setting.
Deinanthe - Clu,p forming to around 45cm high. Suited to damp areas.
Delphinium - One of the most popular groups of perennials, but not grown as often as should be!
Dendranthema - Still so much confusion over this name change. Basically all those plants we know as Chrysanths and just 'Mums' are officially Dendranthema.
Dennstaedtia - Fern - Hardy garden fr\erns for the most part - though deciduous or herbaceous and not evergreen.
Dianthus - group of perennials covering 'Pinks, 'Carnations' and just plain 'Dianthus'!
Diascia - Plant this in the right spot and give it a little winter protection and you will be rewarded well. Not used enough in the perennial border or rock garden.
Dictamnus - A 'must have' perennial with spikes of white or pink flowers. Dictamnus Alba, is known also as the burning bush - but not because of colour, but because of the volatility of the vapour emanating from flowers in hot weather!
Dierama - The wandflower, generally hardy but prefers the protection of light woodland.
Dionysia - Low growing tufts of evergreen foliage, with golden yellow flowers. Suit rock gardens.
Diphylleia - I do not know this, but will investigate!
Dipsacus - The common Teasel, which can be grown as a short-lived perennial - or rightfully as a biennial.
Disporopsis - Think of Solomon's Seal or Polygonatum, and you will have a very good idea as to what this one is.
Disporum - Grow this in light woodland for best effect. Drooping white bell flowers, similar to Lily of the Valley.
Dodecatheon - American Cowslip or Shooting Stars - suited best to light or dappled shade.
Draba - Whitlow Grass - Evergreen cushions of foliage and flowers. Best in full sun - in rockery.
Dracocephalum - Dragon's Head. Some of which are perennials. Winter protection is advisable, and a sheltered position.
Dryas - Mountain Avens - Low growing mat forming clumps for rockery, and well drained soil.
Dryopteris - Hardy Fern - Buckler Fern - A good group of hardy ferns - though not generally evergreen. But, the new foliage in spring is always worth the winter wait!
Duchesnea - Low growing perennial evergreen - best
for novelty value!