Iris tectorum (also known as roof iris, Japanese roof iris and wall iris) is a plant species in the genus Iris, it is also in the subgenus Limniris. It is a rhizomatous perennial. It is native of China, Korea and Burma, with lavender-blue, bluish-violet, purple-blue, blue-lilac or sky blue flowers. There is a white form as well. It is a compact plant and is cultivated as an ornamental plant in temperate regions of the world.
It has a thick,[1] [2] [3] (the size of a man's thumb),[4] creeping,[4] [5] buff (coloured), or greenish rhizome.[6] [7] They are similar in form to a bearded iris rhizome.[8] [9] It has slender, short roots (under the rhizomes),[10] [11] and fibres on the top.[11] The creeping habit, creates spreading clumps of plants.[12] [13] [14] It does not produce stolons.[4]
It has basal fans,[15] [16] that are yellowish green,[11] or pale green,[17] [18] [19] and sword-shaped (ensiform),[7] [20] or lance-shaped.[10] [2] They are also, glossy,[4] [20] [13] and ribbed,[10] [16] [21] and can grow up to between 15- long and 1.5- wide.[16] [22] [23] The leaves are floppy,[19] and described as semi-evergreen.[24] [22] [25]
It has terete (cylindrical),[5] stems that can grow up to between 20- tall.[26] [27] [28] It has 1–2 branches,[6] [19] [22] and 1–2 (reduced) stem leaves.[10] [4] [29]
The stems have 2–3 spathes (leaves of the flower bud), that are green,[5] lanceolate and 3.5- long and 2- wide.[11] [4]
It has a 1 cm long pedicel (flower stalk),[11] which is shorter than the spathe,[4] but similar in size to the ovary.[5]
The stems (and the branches) hold between 1 and 3 flowers,[29] [22] [30] in late spring,[13] [15] [26] or early summer,[1] [15] [18] between April and May,[22] [31] or June.[16] [19] [32] It flowers between September and October in Australia.[33] The flower display can last for 2 weeks.[25] The flowers are 7.6- in diameter,[26] [34] The flattened,[21] [23] [30] horizontal,[35] flowers are larger than Iris japonica flowers.[36]
The flowers come in shades of lavender blue,[30] [28] [35] or bluish violet,[17] [28] [36] or blue-lilac,[21] [34] or purple-blue,[24] [29] [21] or sky blue.[27] [16] [37] There is also a white form.[28] [35] [36]
It has 2 pairs of petals, 3 large sepals (outer petals), known as the 'falls' and 3 inner, smaller petals (or tepals), known as the 'standards'.[3] [7] The falls are obovate (egg-like),[8] [5] or ovate,[11] with darker (or brownish purple/violet).[7] mottling,[1] [16] [21] veining,[6] [20] [38] streaks,[5] [7] or spots,[1] [8] [3] [24] around a toothed or lacinated (fringed),[10] [4] white crest.[38] [34] [36] They have a bi-coloured claw (part of the petal closest to the stem), white and violet or lilac.[4] [5] The falls are 5- long and 4 cm wide.[4] [6] [29] The elliptic standards spread horizontally (not erect),[6] [19] [21] and are 4.5- long and 3 cm wide.[11] [8] Both petals (falls and standards) can have wavy margins.[3] [19] [32]
The flowers are self-fertile,[10] but are pollinated by insects.[20]
It has a 2.5–3 cm long slender, perianth tube,[4] [5] [6] a 2.5 cm long stamen, bright yellow anthers and a cylindric, 1.8–2 cm long ovary.[11] It has a pale bluish-violet style branch, that is 3.5 cm long.[11] It has toothed lobes (at the tips), that are irregular.[5] [6]
After the iris has flowered, between June and August,[11] [17] it produces an ellipsoid or obovoid (oblong-ovoid),[11] [10] light green,[13] seed capsule.[7] [29] It is 4.5- long and 2–2.5 cm wide,[11] [10] [29] and has 6 ribs.[10] When it ripens, (and goes brown,[20]) it splits in three, along 2 or more seams, starting from the top.[10] [29] Inside, are multiple,[20] [29] black-brown seeds,[11] [20] which are pyriform (pear shaped) and have a small cream (coloured) aril (appendage).[11] [10]
In 1994, a study was carried out to isolate various chemical compounds from the seeds of Iris tectorum, it found an ester 'iristectorene B'.[39]
In 1999, a study was carried out Iris tectorum rhizomes, it found a triterpenoid chemical compound.[40]
In 2007, a study was carried out on cytotoxic properties of Iris tectorum, used to treat cancer.[41]
In May 2007, a study was carried out on the rhizomes of Iris tectorum, to find various chemical compounds.[42]
In 2009, a karyotype analysis was carried out on 10 Irises found in China, and found that Iris tectorums was 2n=28.[43]
In 2011, Isoflavones such as tectoridin, iristectorin B and iristectorin A have been found in the rhizomes of Iris tectorum. They were published in the Journal of Chromatography B, Vol. 879, Issue 13, pages 975–980.[44]
In 2012, a study was carried out on the leaves of Iris tectorum for anti cancer properties.[45]
In 2013, a study was carried on Iris tectorum to isolate various chemical compounds.[46]
In 2013, a molecular phylogenetic (genetic evolution) study was carried out on 16 species of Iris found in Korea. It placed Iris mandshurica in a clade with other basal irises, including Iris dichotoma and Iris tectorum.[47]
In January 2014, a study was carried out on the neuro-protective activities of Iris tectorum.[48]
Several isoflavones have been found in Iris tectorum. Iris tectorigenin A is found in Iris florentina, Iris tectorum, Iris pseudacorus, Iris kumaonensis and Belamcanda chinensis (iris domestica). Iristectorin B (C23H24O12) can be found in the rhizomes of Iris tectorum, iris-tectorigenin B found in Iris germanica and Iris tectorum and iristectorin A (which is also found in Belamcanda chinensis).[49]
As most irises are diploid, having two sets of chromosomes, this can be used to identify hybrids and classification of groupings.[3] Diploid counts include 2n=28, Simonet, 1932; 2n=32, Sharma, 1970; 2n=28, Chimphamba, 1973; 2n=28, Karihaloo, 1978; 2n=28, Karihaloo, 1984; 2n=28, Huiang, 1986; 2n=36, Mao & Xue, 1986; 2n=28, Huang 1989; and 2n=32, Dong et al., 1994.[5] It is normally designated as 2 n = 24, 28, 32.[11] [10] [38]
It is pronounced as (Iris) EYE-ris (tectorum) tek-TOR-um.[26] [28]
It is written as 鸢尾 in Chinese script,[11] and known as yuan wei in Pidgin in China.[15] [50]
It has several common names, including; roof iris,[50] [51] [52] Japanese roof iris,[28] [35] [51] wall iris (in America),[52] [53] [54] wall flag,[2] white root iris,[18] [28] Ichihatu (In Japan – meaning first as the first iris to flower),[55] [56] shenan,[50] and roof garden iris.[30]
It is known as Dach-Schwertlilie in German and takiris in Swedish.[50]
The Latin specific epithet tectorum refers to Latin word for roof or covering.[19] [57]
Iris tectorum is native to China, but was first discovered in the 1860s, growing in Japan on the roofs, hence the common name.[25]
It was first published and described by Karl Maximovich in the 'Bulletin of Acad. Imp. Sci. Saint-Pétersbourg' Volume15 page380 in 1871.[4] [58]
It was published in Flor. Serres Vol.22 page 23 in 1874, with a colour illustration,[5] then published by Hooker in Curtis's Botanical Magazine table 6118 in September, 1874,[4] [5] and in the 'Journal of the Royal Horticultural Society' Vol88 page116 in 1963.[6]
It was introduced to England and European cultivation in 1874,[3] [5] by Philipp Franz von Siebold, who sent plants to St Petersburg.[10] It was also introduced to US cultivation by Mr William Bull in 1874.[4] [30]
It was verified by United States Department of Agriculture and the Agricultural Research Service on 2 April 1996 and updated on 1 December 2004.
Iris tectorum is an accepted name by the RHS.[51]
It is native to temperate and tropical regions of Asia.[9] [50]
It is found in (central and south western),[10] [1] [59] China,[34] [50] [51] within the Chinese provinces, of Anhui, Fujian, Gansu, Guangdong, Guangxi, Guizhou, Hainan, Hubei, Hunan, Jiangsu, Jiangxi, Shaanxi, Shanxi, Sichuan, Xizang, Yunnan and Zhejiang.[11]
Also found in Korea,[38] [59] and within (the tropical region) of Myanmar (Burma).[54] [59]
It is often cited as native to Japan,[17] [30] [52] but it may just be naturalized.[1] [8] [22]
It has naturalized in Bhutan and India.[14] It has also naturalized in regions of America, including New Hampshire.[53]
It grows on forest margins, on sunny banks, in meadows, in damp places and beside water.[20] [14] [17] It can also be found growing along roadsides and on steep hillsides, in China.[3] [22]
They can be found at an altitude of 500- above sea level.[11] [9] [14]
In New Hampshire, as a wild flower, it is found on the edges of lawns and fields, beside roadsides and in compost heaps.[53]
The cultivation of Iris tectorum is very similar to that of Iris japonica and Iris milesii.[30]
It is hardy to between USDA Zone 4 and Zone 9.[26] [28] [52] It is hardy to European Zone H2,[6] meaning it can tolerate temperatures as low as −10,[9] but needs protection from hard frosts.[37] Older plants can survive some frosts but young plants need protection in the spring.[34] Both the blue and white forms of the iris, are perfectly hardy.[4] [30] It is hardy in the UK,[2] but it does not flower very well, due to the summers not being hot enough to bake the roots.[31] After flowering, it is best to remove the old stems from Iris confusa, Iris japonica and Iris tectorum, as this helps the plant survive the winter.[9] [60]
It prefers to grow in humus, rich,[23] [37] [54] moist soil,[26] [52] [54] with good drainage.[23] [34] [54]
During spring or autumn, a top dressing of well rotted compost (or well rotted manure),[8] should be added,[10] [34] a feed of fertilizer can also be added.[8] [33] [23] A mulch can also be applied (at the same time) to retain the moisture.[37] [54]
It can tolerate neutral or acidic soils (pH levels between 6.1 – 7.8).[18] [23] [26]
It can tolerate positions between full sun and partial shade,[52] [54] [59] but prefers light shade,[17] [36] [52] In full sun, the leaves can bleach.[8] (similar to woodland conditions).[33] Although, a few sources say it prefers a sunny, sheltered site.[1] [34] [54]
It has average water needs during the growing season.[33] [13] [18] If the summer conditions become exceedingly hot and dry, the iris will go into early dormancy.[20] Therefore it prefers a dry and cold winter, with a warm and wet summer.[4] [22] [34]
It can be grown in a mixed flower border,[13] [18] [23] rock garden,[20] [13] [18] and in a woodland garden.[7] [20] [23] If the plant is to be grown in a rockery, it is recommended that the plant has new soil or fertiliser every year.[34] It can be also grown in containers and large (15 cm) pots,[10] [13] [18] but it needs to be re-potted frequently.[3] In the UK, the pot can survive the winter in a cold greenhouse.[10]
It suffers from a virus disease that causes leaf discolouration,[10] [1] [9] yellowing and streaking.[8] It seems immune to insect pests,[25] [24] but can be prone to damage from slugs or snails.[9] [23] Also an aphid, Aulacorthum solani can be found on the plant.[61]
Since the roots can quickly take all the nutrients out of the soil, division and re-planting is needed every other year,[10] [24] or every 3–5 years when clumps become over-crowded.[3] [12] [33] Although, it can be left undisturbed for many years, but flowering will decrease.[36]
Like most rhizomatous irises, it should be planted with the top of rhizome just at the surface of the soil.[12] [25] [24] They should be spaced 20- apart.[12] [26] [28]
Iris tectorum can be propagated by division or by seed growing.[25] [24] [34] It is easy to raise from seed.[10] [24] [35]
Plants grown from its seeds will re-produce a true form, including white plants.[34]
Division is best done in the spring,[7] [34] or fall (after flowering).[9] [7] [23] Transplanting should be carried out soon after division.[21]
Iris tectorum has many cultivars including;
Like many other irises, most parts of the plant are poisonous (rhizome and leaves), if mistakenly ingested, it can cause stomach pains and vomiting. Also handling the plant may cause a skin irritation (like dermatitis or an allergic reaction.[9] [7]
Despite its toxicity, it is used in Chinese herbal medicine to treat hepatitis and wind damp pains.[63]
The Kam eat fish that have been given fresh Iris tectorum, as medicine to treat stomach aches.[64]
Iris tectorum is commonly called the 'roof iris' because it was grown in the thatch of Chinese and Japanese houses.[32] [37] [36] There are several theories as to why;
The most common theory, was due to a period of wartime,[25] or great famine in Japan, all land was then decreed by the emperor to be cultivated, for rice and other food crops.[33] [23] [31] Also, it was illegal for land to be used for growing flowers.[8] [25] [23] But also women wanted the iris roots for making hair dye, face powder and corn plasters.[36] The rhizomes were ground down,[25] [52] to make a white powder used for whitening the skin,[8] [9] [31] similar in look to Geisha girls.[25] [23] Although, EA bowles did not believe this theory.[36]
Another theory, was that it was grown in the wet clay and was used to bind the straw thatch together, to stop a roof coming apart.[8] [20] [33] It also acted as a decoration, creating a purple flowering roof-ridge.[20]
A final reason known, was that it was planted to avert the 'evil spirits' and a superstition that they prevent disease from affecting the householders.[8] [31]