Leucojum - Snowpake - Sometimes Snowflake. The shorter types get mistaken for Snowdrops, and are similar. Mainly early summer flowering - some earlier - some later - even as late as Autumn.
Leymus - Ornamental Grass - Same as Elymus hispidus is a good blue foliage type.
Lily of the Valley - Convallaria.
Liriope Liriope muscari - Grass - Dense clump of foliage with blue flower spikelets. Makes for good ground cover and does well in most situations. Also a good woodland plant if dappled shade.
Lamium - Good ground covering Dead Nettles - often with ornamental foliage. Short upright clusters of flowers held above the ground-hugging mat of foliage. Mainly evergreen, but sometimes semi-evergreen.
Lathraea - How would you like a parasite in your garden? This one fits the bill! Has no foliage to speak of - just flowers atop the ground in late spring. Needs to be planted near a Willow, Popular or Alders - giving the clue that it needs damp or marshy soil.
Lathyrus - A wide range of sweet peas of course, but here we talk only of the Everlasting Pea - Lathyrus grandiflora. A bit of a rarity in that it is a fully hardy perennial climbing plant.
Lavatera - Many of the mallows are shrubs, sub-shrubs or annuals, but there are some useful perennials as well. The perennial types are best regarded as semi-evergreen, but all are culourful - gaudy even - some of them!
Leontopodium - Had this not had the common name of Edelweiss, the song would have never become popular! Not the showiest of alpine perennials, but will always be used because of its common name! When first introduced to this plant, the reaction is normally "Oh!"
Leptinella - Grow this low growing evergreen perennial for its ground covering qualities. The flowers are an added bonus as they pop out in late spring.
Lespedeza - The Bush Clover. The main perennial is a slightly woody stemmed affair, but with attractive pea flowers (Lespedeza thunbergii). It is sometimes classed as a sub shrub, and does in fact attain a couple of meters in height - and spread. very showy, but best suited to the shrub border, or an empty dry corner somewhere that gets all the sun.
Leucanthemella - Looks very similar to an Aster (Michaelmas Daisy types) Erect with whitish flower through the summer.
Leucanthemum - Some useful alpine perennials in this group - but also some which grow up to 1m tall.
Lewisia - Subtlety goes out of the window with these showy perennials. Normally a rosette of evergreen foliage, with masses of 'bright' flowers through Spring and early Summer. Grow well in walls once established. Hate wet soil in winter.
Liatris - It's main claim to fame is the fact that the flower spikes start to open from the top first, and not as is the norm, the bottom. A colourful perennial with flower spikes to 60cm and tufted grassy foliage.
Libertia - Not the hardiest of 'hardy' perennials, but worth growing for its varied flower colours, and iris-like foliage. Prefers a damp area, though will tolerate dry.
Ligularia - Majestic spikes of golden flowers and large palmate leaves. Prefers damp areas, or even to have its feet in a bog. Heights between 90cm and 1.8m, with a foliage spread of about half its height.
Lilium - this will be a big section once I get roud to writing it! Many different types of Lilies available, and all are showy and desirable.
Limonium - Stattice - Everlasting Flower - Varied colours that ho;ld well after being harvested for dried flowers. They are also very good in the garden.
Linaria - Toadflax. Often mistaken as a miniature snapdragon (Describes it well.) Very slender habit of growth with narrow spikes of flowers not taking too much room.
Lindelophia - Very similar in most respects to Borage. Also goes under the name of Cynoglossum
Linum - Flax - Some are borderline cases between shrub and perennial. But several distinct perennials - notably the powder blue flowered Linum perenne. Dry areas will suit them, but most garden situations in full sun also.
Lithophragma - Woodland Star of the Saxifrage family, so well suited as low growing perennial for woodland situation or under shade of overhanging shrubs. Also good for the rockery.
Lobelia - Perennial Types - Upright spikes encompassing many different colours nowadays. Most of the perennial types are hardy. I have seen these growing in dry areas, borders and at the side of a lake - versatile - and showy!
Lunaria - Honesty - so let's own up to the fact that there is probably only one worth growing as a perennial - Lunaria rediviva. BUT, Honesty - as with foxgloves, readily seeds itself, so is of iuse in perennial or other areas.
Lupinus - The Russell
Lupins are amongst the best of the Perennial Lupins, though there are
other types available. All make a good show year after year - until the
slugs finally get them!
Luzula - Woodrush - This evergreen perennial group, has a few outstanding members for damp areas - Luzula sylvatica Aurea being one of them with golden foliage.
Lychnis - Campion. Thgis is a varied group of good showy perennials with foliage variants from silver ti purple or bronze. There is sure to be one that is good for youm and they all look good in the perennial area.
Lysichiton - Skunk Cabbage is a good common name for this unusual perennial. I have been at close-quarters too many times waiting for the light in order to get a good photo. There are yellow and white types. the yellow has the stronger 'scent'!
Lysimachia - Loosetrife - and you can have ground huggers - trailing even - or upright. The foliage is varied, as are the flower types. Some with upright spikes, others with strange drooping racemes. All in all a good versatile group.