| Turritis glabra | |
|---|---|
 | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Rosids |
| Order: | Brassicales |
| Family: | Brassicaceae |
| Genus: | Turritis |
| Species: | T. glabra |
| Binomial name | |
| Turritis glabra (L.) | |
| Synonyms[2] | |
List
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Turritis glabra, commonly known astower rockcress ortower mustard, is a tall, slim, grey-green plant with small creamy flowers at the top of the stem. It usually grows on poor chalky or sandy soils, in open situations. It is native to Europe, Asia, and North Africa, and it is widespread in North America where it is also probably native. It can be found in many other parts of the world as anintroduced species.
Tower mustard typically reaches 40 to 120 centimeters in height at full growth, but may be stunted to just 30 centimeters or might reach 1.5 meters in height in exceptional circumstances. It is typically abiennial herb, but may occasionally have be a short lived perennial.[3] Plants have a tap-root and fibrous side-roots. Plants usually have several erect, usually unbranched stems which are grey in the lower parts with a covering of simple hairs, but green and glabrous (hairless) above.[4]
The leaves occur in a basalrosette initially, and later grow alternately on the main stem and branches. The basal leaves are blunt and toothed or pinnatifid and up to 15 cm long, whereas the stem and branch leaves become progressively smaller, less divided and more pointed, clasping the stem.[4] The basal leaves are usually covered in hairs (pubescent) on the upper surface, but in rare cases they may be hairless. They vary in shape from spoon shape with a narrow base and wide at the end (spatulate), to being a narrow spear point with the widest point in the middle (oblanceolate), or a rounded rectangle longer than wide (oblong) with a broad point. They are typically 5 to 12 centimeters long, but may be only 4 cm or as much as 15 cm in length. The basal leaves are 1 to 3 centimeters in width.[3]
The leaves on the stems (cauline leaves) are narrowed versions of the spear head shape (blade lanceolate), a somewhat more rounded rectangle (oblong-elliptic), or fully egg shaped with a wider base than end (ovate).[3]
Theinflorescence is a terminalraceme with numerous small, white flowers on small flower stems (pedicels) up to 2 centimeters long. There are four greenishsepals about 5 millimeters long; four pale yellowpetals up to 1.7 cm long; 6stamens and 1 style. The fruit is a greenishsilique up to 8 cm long by 1.7 cm wide, flattened, and held vertically beside the stem.[4]
Turritis glabra was given its first scientific name byCarl Linnaeus in 1753. In 1800 it was moved fromTurritis to genusArabis byJohann Jakob Bernhardi with than nameArabis glabra.[2] Authors such as Hervé Maurice Burdet, James Cullen, and František Dvořák (1921–2016) maintained that the lack of white to purple flowers, not having seeds arranged in a single row in the pod like peas (uniserrately), and not having flattened fruits distinguishes the species inTurritis fromArabis. Botanists maintaining the contrary position such asReed C. Rollins andIhsan Ali Al-Shehbaz point to the ambiguous characteristics of some individuals inTurritis glabra and what they consider more critical features such as similar seed-coat anatomy and chemical similarities such as fatty-acid composition and glucosinolate content.[5] Descriptions of this and other related species in North America in the 19th century accepted the classification inTurritis, but late in the century authors such asAsa Gray were treating it assynonymous withArabis.[6]
As of 2023 the most common classification is asTurritis glabra as listed inPlants of the World Online (POWO),[2]World Flora Online,[7] and in theFlora of North America.[3]
The genus nameTurritis comes from Latin for tower as a reference to the narrow growth of the plant with the leaves and fruits upright and overlapping.[8] Many of its common names similarly reference this such as "tower rockcress",[9] "tower-mustard", and " towercress".[7]
The native distribution of tower mustard is moderately uncertain with sources having some details of its range different. POWO lists it as native to all parts of Europe with the exceptions of Ireland, Sardinia, and Corsica.[2]
They list it as growing in much of the northwest ofTemperate Asia from Turkey and Iran northwards into central Asia and fromChita Oblast,Irkutsk Oblast, andKrasnoyarsk Krai westwards inSiberia. In the more southerly parts of Asia POWO lists it as native to Korea, Japan,Mongolia,Manchuria, north-central China, southeast China,Xinjiang,Nepal, and the westernHimalayas. In addition they list it as introduced toPrimorsky Krai,Sakhalin Island, and theKuril Islands.[2]
In Africa POWO lists it as native toAlgeria,Kenya,Morocco,Rwanda,Tanzania,Uganda, and theDemocratic Republic of the Congo, with it being introduced toLesotho and two parts of South Africa,KwaZulu-Natal, theCape Provinces, and theNorthern Provinces.[2]
In North America POWO lists it as native to all parts of Canada with the exceptions ofNewfoundland and Labrador,Nova Scotia,Prince Edward Island, andNunavut. It is also listed as native to all of the western United States, the north-central US fromMissouri andNebraska northwards, the northeastern US with the exception ofVermont, where they list it as introduced, and in the southeastern US states of Delaware, Kentucky, Maryland, North Carolina, Tennessee, and Virginia.[2]NatureServe disagrees with some of these, not listing it as present in Maryland, present but not evaluated in Vermont, additionally introduced to Kansas, not native to Montana, and also present and evaluated in Georgia. They also do not list it as present in theNorthwest Territories of Canada.[1]
Finally Plants of the World Online lists it as introduced to the Australian states ofNew South Wales andVictoria.[2]
It is classified as anendangered species in the UK and is considered to be facing a very high risk of extinction in the wild. It is listed as a Priority Species under the UKBiodiversity Action Plan. Only 35 sites are recorded byPlantlife mostly inNorfolk, (where 100 plants were found at a new site in 1999) but includes 6 sites nearKidderminster inWorcestershire.
