Brassicaceae (/ˌbræsɪˈkeɪsiːˌiː,-siˌaɪ/) or (the older)Cruciferae (/kruːˈsɪfəri/)[2] is a medium-sized and economically importantfamily offlowering plants commonly known as themustards, thecrucifers, or thecabbage family. Most areherbaceous plants, while some areshrubs. Theleaves are simple (although are sometimes deeply incised), lackstipules, and appear alternately on stems or inrosettes. Theinflorescences are terminal and lackbracts. The flowers have four freesepals, four free alternatingpetals, two shorter freestamens and four longer free stamens. Thefruit has seeds in rows, divided by a thin wall (or septum).
Pieris rapae and other butterflies of the familyPieridae are some of the best-known pests of Brassicaceae species planted as commercial crops.Trichoplusia ni (cabbage looper) moth is also becoming increasingly problematic for crucifers due to its resistance to commonly usedpest control methods.[5] Some rarerPieris butterflies, such asP. virginiensis, depend upon native mustards for their survival in their native habitats. Some non-native mustards such asAlliaria petiolata (garlic mustard), an extremelyinvasive species in the United States, can be toxic to theirlarvae.
Species belonging to the Brassicaceae are mostlyannual,biennial, orperennialherbaceous plants, some aredwarf shrubs orshrubs, and very fewvines. Although generally terrestrial, a few species such aswater awlwort live submerged in fresh water. They may have ataproot or a sometimes woodycaudex that may have few or many branches, some have thin or tuberousrhizomes, or rarely developrunners. Few species have multi-cellular glands.Hairs consist of one cell and occur in many forms: from simple to forked, star-, tree- or T-shaped, rarely taking the form of a shield or scale. They are never topped by a gland. Thestems may be upright, rise up towards the tip, or lie flat, are mostly herbaceous but sometimes woody. Stems carry leaves or the stems may be leafless (inCaulanthus), and some species lack stems altogether. The leaves do not havestipules, but there may be a pair of glands at base ofleaf stalks andflower stalks. The leaf may be seated or have a leafstalk. Theleaf blade is usually simple, entire ordissected, rarelytrifoliolate orpinnately compound. A leaf rosette at the base may be present or absent. The leaves along the stem are almost alwaysalternately arranged, rarely apparently opposite.[6] The stomata are of theanisocytic type.[7] Thegenome size of Brassicaceae compared to that of other Angiosperm families is very small to small (less than 3.425 million base pairs per cell), varying from 150 Mbp inArabidopsis thaliana andSphaerocardamum spp., to 2375 MbpBunias orientalis. The number ofhomologous chromosome sets varies from four (n=4) in somePhysaria andStenopetalum species, five (n=5) in otherPhysaria andStenopetalum species,Arabidopsis thaliana and aMathiola species, to seventeen (n=17). About 35% of the species in which chromosomes have been counted have eight sets (n=8). Due topolyploidy, some species may have up to 256 individual chromosomes, with some very high counts in the North American species ofCardamine, such asC. diphylla.Hybridisation is not unusual in Brassicaceae, especially inArabis,Rorippa,Cardamine andBoechera. Hybridisation between species originating in Africa and California, and subsequentpolyploidisation is surmised forLepidium species native to Australia and New Zealand.[8]
Typicalfloral diagram of a Brassicaceae (Erysimum "Bowles' Mauve")
Flowers may be arranged inracemes,panicles, orcorymbs, with pedicels sometimes in the axil of a bract, and few species have flowers that sit individually on flower stems that spring from the axils of rosette leaves. The orientation of the pedicels when fruits are ripe varies dependent on the species. The flowers arebisexual,star symmetrical (zygomorphic inIberis andTeesdalia) and theovary positioned above the other floral parts. Each flower has four free or seldom mergedsepals, the lateral two sometimes with a shallow spur, which are mostly shed after flowering, rarely persistent, may be reflexed, spreading, ascending, or erect, together forming a tube-, bell- or urn-shaped calyx. Each flower has fourpetals, set alternating with the sepals, although in some species these are rudimentary or absent. They may be differentiated into ablade and aclaw or not, and consistently lack basal appendages. The blade is entire or has an indent at the tip, and may sometimes be much smaller than the claws. The mostly sixstamens are set in two whorls: usually the two lateral, outer ones are shorter than the four inner stamens, but very rarely the stamens can all have the same length, and very rarely species have different numbers of stamens such as sixteen to twenty four inMegacarpaea, four inCardamine hirsuta, and two inCoronopus. The filaments are slender and not fused, while the anthers consist of two pollen producing cavities, and open with longitudinal slits. The pollen grains aretricolpate. Thereceptacle carries a variable number ofnectaries, but these are always present opposite the base of the lateral stamens.[6][9]
There is onesuperiorpistil that consists of twocarpels that may either sit directly above the base of the stamens or on astalk. It initially consists of only one cavity but during its further development a thin wall grows that divides the cavity, both placentas and separates the two valves (a so-called false septum). Rarely, there is only one cavity without a septum. The 2–600ovules are usually along the side margin of the carpels, or rarely at the top. Fruits are capsules that open with two valves, usually towards the top. These are calledsilique if at least three times longer than wide, orsilicle if the length is less than three times the width. The fruit is very variable in its other traits. There may be one persistentstyle that connects the ovary to the globular or conicalstigma, which is undivided or has two spreading or connivent lobes. The variously shaped seeds are usually yellow or brown in color, and arranged in one or two rows in each cavity. Theseed leaves are entire or have a notch at the tip. The seed does not containendosperm.[6]
Brassicaceae have a bisymmetrical corolla (left is mirrored by right, stem-side by out-side, but each quarter is not symmetrical), a septum dividing the fruit, lackstipules and have simple (although sometimes deeply incised) leaves. Thesister familyCleomaceae hasbilateral symmetrical corollas (left is mirrored by right, but stem-side is different from out-side), stipules and mostly palmately divided leaves, and mostly no septum.[6] Capparaceae generally have agynophore, sometimes anandrogynophore, and a variable number of stamens.[9]
Almost all Brassicaceae haveC3 carbon fixation. The only exceptions are a fewMoricandia species, which have a hybrid system between C3 andC4 carbon fixation, C4 fixation being more efficient in drought, high temperature and low nitrate availability.[10] Brassicaceae contain different cocktails of dozens ofglucosinolates. They also contain enzymes calledmyrosinases, that convert the glucosinolates intoisothiocyanates,thiocyanates andnitriles, which are toxic to many organisms, and so help guard against herbivory.[11]
Carl Linnaeus in 1753 regarded the Brassicaceae as a natural group, naming them "Klass" Tetradynamia.Alfred Barton Rendle placed the family in the orderRhoeadales, whileGeorge Bentham andJoseph Dalton Hooker in their system published from 1862 to 1883, assigned it to their cohortParietales (now the classViolales). Following Bentham and Hooker,John Hutchinson in 1948 and again in 1964 thought the Brassicaceae to stem from near thePapaveraceae. In 1994, a group of scientists includingWalter Stephen Judd suggested to include theCapparaceae in the Brassicaceae. Early DNA-analysis showed that the Capparaceae—as defined at that moment—wereparaphyletic, and it was suggested to assign the genera closest to the Brassicaceae to theCleomaceae.[12] The Cleomaceae and Brassicaceae diverged approximately 41 million years ago.[8] All three families have consistently been placed in one order (variably calledCapparales orBrassicales).[12] TheAPG II system merged Cleomaceae and Brassicaceae. Other classifications have continued to recognize the Capparaceae, but with a more restricted circumscription, either includingCleome and its relatives in the Brassicaceae or recognizing them in the segregate familyCleomaceae. TheAPG III system has recently adopted this last solution, but this may change as a consensus arises on this point. Current insights in the relationships of the Brassicaceae, based on a 2012 DNA-analysis, are summarized in the following tree.[9][13]
Early classifications depended on morphological comparison only, but because of extensiveconvergent evolution, these do not provide a reliablephylogeny. Although a substantial effort was made throughmolecular phylogenetic studies, the relationships within the Brassicaceae have not always been well resolved yet. It has long been clear that theAethionema aresister of the remainder of the family.[14] One analysis from 2014 represented the relation between 39 tribes with the following tree.[15][needs update]
Brassicaceae can be found almost on the entire land surface of the planet, but the family is absent from Antarctica, and also absent from some areas in the tropics i.e. northeastern Brazil, theCongo basin,Maritime Southeast Asia and tropicalAustralasia. The area of origin of the family is possibly theIrano-Turanian region, where approximately 900 species occur in 150 different genera. About 530 of those 900 species areendemics. Next in abundance comes theMediterranean region, with around 630 species (290 of which are endemic) in 113 genera. The family is less prominent in theSaharo-Arabian region—65 genera, 180 species of which 62 are endemic—and North America (comprising theNorth American Atlantic region and theRocky Mountain floristic region)—99 genera, 780 species of which 600 are endemic. South America has 40 genera containing 340 native species, Southern Africa 15 genera with over 100 species, and Australia and New-Zealand have 19 genera with 114 species between them.[8]
Brassicaceae are almost exclusivelypollinated by insects. A chemical mechanism in the pollen is active in many species to avoidselfing. Two notable exceptions are exclusiveself-pollination in closed flowers inCardamine chenopodifolia, and wind pollination inPringlea antiscorbutica.[9] Although it can be cross-pollinated,Alliaria petiolata (garlic mustard) isself-fertile. Most species reproduce sexually through seed, butCardamine bulbifera producesgemmae and in others, such asCardamine pentaphyllos, the coral-like roots easily break into segments, that will grow into separate plants.[9] In some species, such as in the genusCardamine, seed pods open with force and so catapult the seeds quite far. Many of these have sticky seed coats, assisting long-distance dispersal by animals, and this may also explain several intercontinental dispersal events in the genus, and its near global distribution. Brassicaceae are common onserpentine anddolomite rich inmagnesium. Over a hundred species in the family accumulateheavy metals, particularlyzinc andnickel, which is a record percentage.[19] SeveralAlyssum species can accumulate nickel up to 0.3% of their dry weight, and may be useful insoil remediation or evenbio-mining.[20]
Brassicaceae containglucosinolates as well asmyrosinases inside their cells. When the cell is damaged, the myrosinaseshydrolise the glucosinolates, leading to the synthesis ofisothiocyanates, which arecompounds toxic to most animals, fungi and bacteria. Some insect herbivores have developed counter adaptations such as rapid absorption of the glucosinates, quick alternative breakdown into non-toxic compounds and avoiding cell damage. In the whites family (Pieridae), one counter mechanism involves glucosinolate sulphatase, which changes the glucosinolate, so that it cannot be converted to isothiocyanate. A second is that the glucosinates are quickly broken down, forming nitriles.[11] Differences between the mixtures of glucosinolates between species and even within species is large, and individual plants may produce in excess of fifty individual substances. The energy penalty for synthesising all these glucosinolates may be as high as 15% of the total needed to produce a leaf.Barbarea vulgaris (bittercress) also producestriterpenoid saponins. These adaptations and counter adaptations probably have led to extensive diversification in both the Brassicaceae and one of its major pests, the butterfly familyPieridae. A particular cocktail of volatile glucosinates triggers egg-laying in many species. Thus a particular crop can sometimes be protected by planting bittercress as a deadly bait, for the saponins kill the caterpillars, but the butterfly is still lured by the bittercress to lay its egg on the leaves.[21]A moth that feeds on a range of Brassicaceae is thediamondback moth (Plutella xylostella). Like the Pieridae, it is capable of converting isothiocyanates into less problematicnitriles. Managing this pest in crops became more complicated after resistance developed against a toxin produced byBacillus thuringiensis, which is used as a wide spectrum biologicalplant protection against caterpillars.Parasitoid wasps that feed on such insect herbivores are attracted to the chemical compounds released by the plants, and thus are able to locate their prey. Thecabbage aphid (Brevicoryne brassicae) stores glucosinolates and synthesises its own myrosinases, which may deter its potential predators.[19]
Since its introduction in the 19th century,Alliaria petiolata has been shown to be extremely successful as aninvasive species in temperate North America due, in part, to its secretion of allelopathic chemicals. These inhibit thegermination of most competing plants and kill beneficial soilfungi needed by many plants, such as many tree species, to successfully see their seedlings grow to maturity. Themonoculture formation of an herb layer carpet by this plant has been shown to dramatically alter forests, making them wetter, having fewer and fewer trees, and having more vines such as poison ivy (Toxicodendron radicans). The overall herb layerbiodiversity is also drastically reduced, particularly in terms ofsedges andforbs. Research has found that removing 80% of the garlic mustardinfestation plants did not lead to a particularly significant recovery of thatdiversity. Instead, it required around 100% removal. Given that not one of an estimated 76species thatprey on the plant has been approved forbiological control inNorth America and the variety of mechanisms the plant has to ensure its dominance without them (e.g. high seed production, self-fertility,allelopathy, spring growth that occurs before nearly all native plants, roots that break easily when pulling attempts are made, a complete lack of palatability for herbivores at all life stages, etc.) it is unlikely that such a high level of control can be established and maintained on the whole.[22][23][24][25][26] It is estimated that adequate control can be achieved with the introduction of two Europeanweevils, including one that ismonophagous.[27][28] TheUSDA's TAG group has blocked these introductions since 2004.[29] In addition to being invasive, garlic mustard also is a threat to native North AmericanPieris butterflies[24][30] such asP. oleracea, as they preferentiallyoviposit on it, although it is toxic to theirlarvae.
Invasive aggressive mustard species are known for being self-fertile, seeding very heavily with small seeds that have a lengthy lifespan coupled with a very high rate of viability and germination, and for being completely unpalatable to both herbivores and insects in areas to which they are not native. Garlic mustard is toxic to several rarer North AmericanPieris species.
Pringlea antiscorbutica, commonly known as Kerguelen cabbage, is edible, containing high levels ofpotassium. Its leaves contain a vitamin C-rich oil, a fact which, in the days of sailing ships, made it very attractive to sailors suffering fromscurvy, hence the species name's epithetantiscorbutica, which means "against scurvy" inLow Latin. It was essential to the diets of the whalers onKerguelen when pork, beef, orseal meat was used up.
^Turini TA, Daugovish O, Koike ST, Natwick ET, Ploeg A, Dara SK, Fennimore SA, Joseph S, LeStrange M, Smith R, Subbarao KV, Westerdahl BB. Revised continuously.UC IPM Pest Management Guidelines Cole Crops. UC ANR Publication 3442. Oakland, CA.
^abcdAl-Shehbaz, I.A. (2012)."Neotropical Brassicaceae".Neotropikey—Interactive key and information resources for flowering plants of the Neotropics. Retrieved2017-07-12.
^Metcalfe, C.R.; Chalk, L. (1950).Anatomy of Dicotyledons. Vol. 1: Leaves, Stem, and Wood in relation to Taxonomy, with notes on economic Uses. Oxford At The Clarendon Press. pp. 79–87.
^abcdRenate Schmidt; Ian Bancroft, eds. (2010).Genetics and Genomics of the Brassicaceae. Plant Genetics and Genomics: Crops and Models. Vol. 9. Springer Science & Business Media.
^Guarino, Carmine; Casoria, Paolo; Menale, Bruno (2000). "Cultivation and use of isatis tinctoria L. (Brassicaceae) in Southern Italy".Economic Botany.54 (3):395–400.doi:10.1007/bf02864789.S2CID42741171.
^Binney, Ruth (2012).The Gardener's Wise Words and Country Ways. David & Charles.ISBN978-0715334232.
Arias, Tatiana; Pires, J. Chris (October 2012). "A fully resolved chloroplast phylogeny of the brassica crops and wild relatives (Brassicaceae: Brassiceae): Novel clades and potential taxonomic implications".Taxon.61 (5):980–988.doi:10.1002/tax.615005.
