They are separate varieties but both originared in Japan. 100's of years of hybridizing in Asia, Europe and the US have produced many, many variations. Except for dwarf varieties, both are large growing and not terribly cold hardy.

The plants are very similar, but their history is very different. Kurume azaleas are the result of many generations of breeding for use in a climate with lows of about +5° F. They are typically dense low growing bushes. On the other hand, Belgian Indicas were propagated to be grown in greenhouses and sold as house plants. Some of these were hybridized with hardier plants to be grown in the Southern US, becoming the Southern Indicas. When grown as garden plants, they tend to be taller and larger plants.

Kurume azaleas were bred at Kurume, an inland town in Kyushu, which is the southernmost of the four main islands of Japan. The ancestral forms, were brought early in the 19th century from sacred Mt Kirishima, and from them seedlings were raised and propagated by Motozo Sakamoto. On his death the collection passed to Kijiro Akashi, who developed the race and is said to have raised most of those in cultivation. The azaleas of Mt Kirishima, are very variable in the size and persistence of their leaves, and also in their flowers, which 'vary a little in size, in degree of fragrance and greatly in color; the most common shades are rosy mauve to magenta, but salmon and salmon-red are plentiful; pink, scarlet and crimson are rather rare. Plants bearing white flowers are occasionally found'. The two species that grow on the mountain are R. kiusianum and R. kaempferi, and it is now thought that the polymorphism of the Kirishima azaleas is due to hybridization between them. Some of the Kurume azaleas show the influence of R. kaempferi quite strongly, but others, especially those with white or pale pink flowers, are very different from authentic R. kiusianum as grown in this country, yet show no influence of R. kaempferi. There appears to be some other element in the race, and it is suggested that this may be R. sataense.

In the 19th century Kurume was remote from the main horticultural centers, and its azaleas were scarcely known, even in Japan itself, but early in this century a few reached Europe through the Yokohama Nursery Company, and others were imported by Dutch nurserymen. Among these were two of the most famous: 'Hinomayo' and 'Hinodegiri'. Apart from these, the Kurumes grown in Britain belong to the 'Wilson Fifty', so called because they were selected from Asahi's collection by the great plant-collector E. H. Wilson when he visited Kurume in 1918. Two sets of these fifty varieties (out of the 250 then grown) were bought by him for the Arnold Arboretum, where they were propagated and further distributed. Wilson gave English names to his Fifty, which are not translations from the Japanese but invented by him. They are rarely used, the Japanese names being more memorable, even if difficult to pronounce correctly.

Kurume azaleas are not widely grown, partly because they are thought to be tender. A few are definitely tender, but these have mostly dropped out of commerce; the rest are hardier than generally supposed, though like many other evergreen azaleas they may suffer damage from frost when young. The flowers are small, but borne in wonderful profusion in late April or May. In several varieties the calyx is petaloid, i.e., converted into a sort of outer corolla, colored and marked like the true corolla. Although the result of several generations of breeding, they have retained the dense and comparatively dwarf habit of their wild ancestors. They tolerate full sun, and woodland conditions are quite alien to their nature.

Kurume azaleas are hardy to Zone 7, +5° F. After five to eight years in the garden, most Kurume azaleas become dense 18- to 30-inch bushes with small glossy leaves. In spring the foliage is hidden by 1-inch flowers. Typical varieties are 'Coral Bells', medium pink; 'Eureka', similar to 'Coral Bells' but hardier; 'Glory', salmon pink; 'Hershey's Red', rose red; 'Hino Crimson', crimson; 'Hinode Giri', bright red; 'Lorna', bright pink; 'Polar Bear', white and 'Snow', white. For hardiness: 'Blaauw's Pink' salmon pink; and Karen', dark lavender, are hardy to Zone 6, -5° F.

The Indica or Belgian Indian azaleas are divided into two groups according to their hardiness. The Belgian Indicas were developed as house plants in the 1800s and are generally hardy to Zone 10, +35° F; Southern Indicas were developed from plants at Magnolia Plantation in Charleston, S.C. and are generally hardy to Zone 8, +15° F. Both types may become 6 feet tall and 10 feet or more across after 5 to 10 years in the garden. The flowers, especially of the Belgian Indica type, are apt to be frilled at the edge or many-petaled double blossoms and often are 2 to 3 inches across. Typical Belgian Indica varieties are: 'Alaska', snow white, two layers of petals; 'Albert and Elizabeth', white, edged pink, double; 'Avenir', salmon pink, double; 'California Sunset', variegated white and pink, double; and 'Fire Dance', fiery red, double. Typical Southern Indicas, all with single blossoms having one layer of petals, are 'Brilliant', red; 'Duc de Rohan', salmon pink; 'Fielder's White', snow white; 'Prince of Wales', cherry red; ´Formosa´, (deep magenta-purple flowers); ´George Lindley Tabor´, (white flowers with purplish-pink blotch and purple throat); ´Delaware Valley White´, (pure white flowers with ruffled petals); and 'Southern Charm', deep rose pink. For hardiness: 'Formosa', also called 'Phoenicia', lavender, is hardy to Zone 6, -5° F.

Wow, what a post.

Can you tell me what 'Kirin' is?

My memory tells me that we called it Azalea indica but when I google it, it comes up as Azalea kurume and Azalea indica. Whatever they were, they did very well in our cold frosty winters and back then, 2-3 decades ago, we did have severe frosts.

In Spring, they would be covered in flowers.

Sometimes there would be a more 'elegantly' shaped plant (not as hard-pruned I think). Slender branches reaching upwards, wearing her flowers and her leaves like a dress. I could never decide with I preferred: smothered in pink or scattered pieces of pink and green; though I think, really, it was the latter.

Also, does 'Kirin' have the hose-in-hose style of flower? Google says yes but then is Google to be trusted?? I'm not overly fond of this hose-in-hose business. And I cannot remember what those long-ago Kirin's had.

According to the ARS website and other sources the familiar hose-in-hose ‘Coral
Bells’ and 'Daybreak' are synonymous with ‘Kirin,’ a plant
introduced by both Wilson (#22) and the Domoto
Brothers around 1918. It is hardy to 0F. The parents are unknown, but as with most Kurumes, they show signs as being a mix of R. kaempferi and R. sataense; as well as the naturally occurring hybrid: R.x'obtusum' which is probably R. kiusianum var kiusianum x R. kaempferi.

Kirin is a Kurume hybrid that was introduced first by the Domoto brothers in California and later by Wilson and others in the US as Coral Bell. It is hardy to 5 below zero (colder part of Zone 7).