the present invention ‘ metolius ’ is a new and distinct variety of a mentha canadensis plant having the following characteristics that , in combination , are not exhibited in other m . canadensis plants . l - menthone to d - isomenthone ratio of around 4 . 5 %, typical of that found in commercial peppermint ( mentha piperita ) oil . in other commercial mentha canadensis , this ratio is around 2 . 0 % or less . l - menthone of about 18 % to 20 %, compared to about 8 % to 10 % for other commercial m . canadensis . l - menthol of about 62 %, this compared to 42 % and 72 % for commercial peppermint and other commercial m . canadensis respectively . l - limonene of about 2 . 5 % compared to 1 . 5 % and under 2 . 0 % for peppermint and other commercial m . canadensis respectively . when grown side by side with other commercial m . canadensis , ‘ metolius ’ is a slightly shorter plant with leaves slightly darker , shorter , and narrower . botanical description : m . canadensis ‘ metolius ’ is an herbaceous perennial with an upright shrubby growth habit . the plant physically spreads by stolons and it is reasonable for a single rooted cutting to spread and cover 3 - 4 square feet after one growing season . numerous branching stems are produced each year with an eventual height of 70 - 80cm . compared to ‘ shivalik ’ ( not patented ) and ‘ kosi ’ ( u . s . plant pat . no . 12 , 426 ), two commonly grown commercial cornmints , the plant is slightly shorter with darker green leaves when grown under similar growing conditions . the leaves are also slightly longer and narrower compared to ‘ shivalik .’ it matures about the same time as ‘ shivalik ’ and ‘ kosi .’ ‘ metolius ’ has been grown in different field locations . it has also been grown under greenhouse conditions . asexual propagation through stem and rhizome cuttings have been successfully carried out many times since 2002 at the applicants &# 39 ; facilities in eugene , oreg . and sunnyside , wash . the resulting propagules have remained stable in appearance , oil quality , and other characteristics to the original plant . the basic morphological characteristics have remained consistent , with any minor differences easily attributed to differences such as climate , soils , fertilizer , or water regime . the distinguishing traits present in ‘ metolius ’ remain constant in the asexually reproduced plants . oil composition and flavor : although ‘ metolius ’ has the same chemical components as other m . canadensis varieties , the relative amount of several components resembles the distribution typically found with peppermint oil . the l - menthone / d - isomenthone ratio of about 4 . 5 for ‘ metolius ’ is typical of a standard mentha piperita which contributes to the clean peppermint - like flavor characteristics noted with this oil . the level of l - menthone is about 18 . 0 % for both ‘ metolius ’ and commercial peppermint compared to 10 % for other commercial m . canadensis varieties . the level of l - menthol is about 62 %, for ‘ metolius ’ compared with 42 % and 72 % for peppermint and other commercial m . canadensis , respectively . the l / limonene level for ‘ metolius ’ is about 2 . 5 % compared to 1 . 5 % and less than 2 . 0 % for peppermint and other commercial m . canadensis respectively . stem and leaves : ‘ metolius ’ has a square stem and therefore does not have a stem diameter . the stem dimensions measure 8 - 9 mm long per side of the square for a total dimension of 8 - 9 mm by 8 - 9 mm when mature . measurements were taken near the base of the stem , since this measurement will decrease towards the tip of the plant . the plant matures to approximately 70 - 80 cm in length . internode length varies considerably along the stem from less than 20 mm near the base and at the apex , increasing to an average of 50 mm along the midstem . under crowded conditions , internode length can even be higher , up to 80 mm . as a mint plant , ‘ metolius ’ spreads by underground stolons and the number of stems is highly variable . stems and ovate leaves are pubescent , oppositely arranged on the stem with an equilateral base , an acute apex , serrate margin and decreasing in size towards the apex of a blooming stem . the average mature leaf length is 60 mm . average leaf width is 30 mm . venation pattern is pinnate . dorsal leaf surface color is medium yellow green ( 147a — yellow - green group ), with a lighter ventral color ( 147b — yellow - green group ). vein color is light yellow green ( 147c — yellow green group ). the mature petiole length is 6 - 8 mm . petiole width is 3 - 4 mm . petiole thickness is 1 - 2 mm . petiole color is light yellow green ( 147c — yellow - green group ). stem color is also light yellow green ( 1460 — yellow - green group ). color numbers are from the r . h . s . colour chart ( royal horticultural society ( great britain ), london 1966 ). the base of the stem has a more “ woody ” appearance and quality with more brownish coloring and fissures . the fragrance is a clean peppermint - like aroma . flower : like other mentha canadensis species , ‘ metolius ’ possesses a flower spike with a pair of bract - like leaves subtending each verticillaster . the individual flowers contain a 4 - lobed , nearly regular , mostly white , tubular corolla with a slight light purple coloration near the base ( 85c — violet group ). the flower is 8 mm long from the base of the calyx to the tip of the forked white stigma . the calyx generally has five teeth fused at the base forming a short tube and is 3 mm long . the calyx , peduncle and pedicel colors are light yellow green ( 147c — yellow - green group ). each flower has one pistil with an 8 mm long white style and four epipetalous stamens that are exerted with 4 mm long white filaments . the white anthers are less than 1 mm . pollen is not produced in abundance . that which is produced has a pale yellow color . the formation of seed is a rare event . there is no obvious flower fragrance . the above description is based on observations of a field plot made during the middle of the second growing season of the field plot outdoors in western oregon . genetic analysis : in order to determine the precise genetic identity of ‘ metolius ’, dna ( ssr ) microsatellite marker analysis was conducted using known methods as described by t . a . holton , plant genotypizng by analysis of microsatellites 15 - 28 , in plant genotyping : the dna fingerprinting of plants ( r . h . henry ed ., 2001 ). comparing microsatellite dna ( ssr ) methodologies with other dna genotyping techniques such as rflps , aflps , and rapds , has established that microsatellite dna ( ssr ) offers a more reliable , repeatable method for characterization with an increased ability to differentiate among plant varieties . the technique has been widely used in animal , plant , and human identification and population studies . the drawback of the technique is the initial high cost of developing the markers . however , once these markers have been developed , they can be simply used by combining pcr with genscan technologies . during 2003 - 2005 period , a project was conducted using 34 microsatellite markers to genetically identify ‘ metolius .’ a total of 4 different populations of m . canadensis were collected . their microsatellite dna profiles were then compared against a total of 8 recognized peppermint varieties along with other closely related mentha species including spearmint ( m . spicata ). a total of 179 microsatellite characters / profiles were found from the 34 markers . genetic distances as measured by total character differences among different populations of the same variety ranged from 0 - 14 . the values among recognized peppermint varieties ranged from 16 - 42 . the values between ‘ metolius ’ populations and other m . canadensis populations ranged from 0 - 4 . a phylogenetic analysis was conducted as well as a principal component analysis . both revealed that ‘ metolius ’ and m . canadensis populations clustered together and formed a strongly supported m . canadensis species group . based on these genetic analyses , ‘ metolius ’ was classified as a variety of m . canadensis . the differences observed among the m . canadensis samples are typical of the differences noted among different varieties of the same species , and allow the identification of ‘ metolius ’ from other varieties of m . canadensis . plant disease resistance / susceptibility : observations of ‘ metolius ’ since 2002 indicate that rust does not infect ‘ metolius ’ under any observed circumstances . furthermore , ‘ metolius ’ has exhibited high tolerance to verticillum wilt through the same observation period . winter hardiness and drought / heat tolerance : ‘ metolius ’ is winter hardy and heat tolerant in the common mint growing regions of the world . no specific claims are made to exceptional cold hardiness or heat tolerance .
a new and distinct variety of mentha canadensis is characterized by its unique oil chemistry and flavor profile resembling that of peppermint oil , and by its tolerance to verticillium wilt and mint rust . dna microsatellite marker analysis has shown that ‘ metolius ’ is a distinct variety of m . canadensis .