Belongs within: Anthemideae.
Contains: Artemisia section Tridentatae.
Artemisia, including sagebrushes and wormwoods, is a mostly Northern Hemisphere genus of usually strong-smelling, wind-pollinated herbs and shrubs. Notable species include wormwood A. absinthium, used to make the spirit absinthe, and tarragon A. dracunculus, used as a culinary herb. Plants have discoid or disciform capitula with all florets hermaphroditic or with central florets functionally male.
Herbs of dragons and worms
Published 14 November 2021
Preparing for this post has inspired me to some low-key experimentation. When it came time to assign myself its topic, I landed on the plant genus Artemisia. This is the genus that, among others, includes the culinary herb tarragon, Artemisia dracunculus. Which got me thinking that I wasn’t sure if I’d ever actually eaten tarragon. I asked Christopher if he was familiar with it; he responded that all he knew about tarragon was that you had to consume it in the 1970s. Without access to a functioning Delorean, I did the next best thing and prepared a dish of tarragon chicken myself. The verdict: very tasty, though I could appreciate why tarragon might have a reputation for being somewhat difficult as it had a light flavour that I could imagine being easily overwhelmed.
Tarragon is not the only species of Artemisia of significance to humans. This genus of composite-flowered plants comprsises over five hundred species and subspecies of herbs and small shrubs. The greatest diversity is found in arid and semi-arid regions of the Northern Hemisphere temperate zone (Sanz et al. 2008). The genus is characterised by its distinctive pollen with surface spinules reduced or absent. This pollen type is associated with the wind pollination typical of the genus, though some species do exhibit features such as sticky pollen and colourful flower-heads associated with insect visitation (Hayat et al. 2009). The flower-heads or capitula (a reminder that the ‘flowers’ of composite plants such as daisies and thistles actually represent a fusion of multiple flowers) of Artemisia are either disciform, with an outer circle of reduced ray florets surrounding the inner disc florets, or discoid, with disc florets only. In disciform capitula, the outer limb of the ray florets is reduced to a membranous vestige, not readily visible without minute examination. The ray florets are female whereas the disc florets are ancestrally hermaphroditic (more on that shortly). In discoid capitula, where the ray florets have been lost, all florets are uniformly hermaphroditic.
Historically, there has been some variation in the classification of Artemisia but a popular system divides the genus between five subgenera. A phylogenetic analysis of Artemisia and related genera by Sanz et al. (2008) found that the genus as currently recognised is not monophyletic, with a handful of small related genera being embedded within the clade. Time will tell whether this inconsistency is resolved by subdividing Artemisia or simply rolling in these smaller segregates, but for the purposes of this post they can be simply set aside. The subgenus Dracunculus, including tarragon and related species, falls in the sister clade to all other Artemisia. As well as being united by molecular data, members of this clade are distinguished by disciform capitula in which the central disc florets have become functionally male (female organs have been rendered sterile).
The second clade encompasses the subgenera Artemisia and Absinthium, with disciform capitula, and Seriphidium and Tridentatae, with discoid capitula. Not all authors have supported the distinction of Artemisia and Absinthium, and Sanz et al. identify both as non-monophyletic, both to each other and to the discoid subgenera. Because of their similar flower-heads, most authors have presumed a close relationship between the Eurasian Seriphidium and the North American Tridentatae (commonly known as sagebrushes). Some have even suggested the former to be ancestral to the latter. However, Sanz et al.‘s results questioned such a relationship, instead placing the Tridentatae species in a clade that encompassed all the North American representatives of the Artemisia group.
As well as the aforementioned tarragon, economically significant representatives of Artemisia include wormwood A. absinthium, best known these days as the flavouring agent of absinthe (though historically it has also been used for more innocuous concoctions). Mugworts (A. vulgaris and related species) have also been used for culinary and medicinal purposes. Sagebrushes are a dominant component of the vegetation in much of the Great Basin region of North America, providing crucial habitat for much of the region’s wildlife. Artemisia species have shaped the lives of many of their co-habitants, both animal and human.
Systematics of Artemisia
Characters (from L. M. Shultz): Annuals, biennials, perennials, subshrubs, or shrubs, 3–350 cm (usually, rarely not, aromatic). Stems 1–10+, usually erect, usually branched, glabrous or hairy (hairs basi- or medifixed). Leaves basal or basal and cauline; alternate; petiolate or sessile; blades filiform, linear, lanceolate, ovate, elliptic, oblong, oblanceolate, obovate, cuneate, flabellate, or spatulate, usually pinnately and/or palmately lobed, sometimes apically ± 3-lobed or -toothed, or entire, faces glabrous or hairy (hairs multicelled and filled with aromatic terpenoids and/or 1-celled and hollow, dolabriform, T-shaped). Heads usually discoid, sometimes disciform (subradiate in A. bigelovii), in relatively broad, paniculiform arrays, or in relatively narrow, racemiform or spiciform arrays. Involucres campanulate, globose, ovoid, or turbinate, 1.5–8 mm diam. Phyllaries persistent, 2–20+ in 4–7 series, distinct, (usually green to whitish green, rarely stramineous) ovate to lanceolate, unequal, margins and apices (usually green or white, rarely dark brown or black) ± scarious (abaxial faces glabrous or hairy). Receptacles flat, convex, or conic (glabrous or hairy), epaleate (rarely paleate). Ray florets absent(peripheral pistillate florets in disciform heads usually 1–20, their corollas filiform; corollas of 1–3 pistillate florets in heads of A. bigelovii sometimes ± 2-lobed, weakly raylike). Disc florets 2–20(–30+), bisexual and fertile, or functionally staminate; corollas (glabrous or ± hirtellous) usually pale yellow, rarely red, tubes ± cylindric, throats subglobose or funnelform, lobes 5, ± deltate. Cypselae (brown) fusiform, ribs 0 (and faces finely striate) or 2–5, faces glabrous or hairy (not villous), often gland-dotted (pericarps sometimes with myxogenic cells, without resin sacs; embryo sac development monosporic); pappi usually absent (rarely coroniform, sometimes on outer in A. rothrockii). x = 9.
<==Artemisia Linnaeus 1778M79 |--A. subg. ArtemisiaM79 | | i. s.: A. californicaM79 | | A. frigidaM79 | | A. ludovicianaM79 | | |--A. l. ssp. ludovicianaH93 | | |--A. l. ssp. albulaH93 | | |--A. l. ssp. candicansH93 | | `--A. l. ssp. incomptaH93 | |--A. sect. ArtemisiaTV01 | | |--A. armeniacaTV01 | | |--A. biennisTV01 | | |--A. chamaemelifoliaTV01 | | |--A. incanaTV01 | | |--A. tournefortianaTV01 | | `--A. vulgarisTV01 | `--A. sect. AbsinthiumM79 | |--A. austriacaTV01 | | |--A. a. var. austriacaTV01 | | `--A. a. var. advenaTV01 | `--A. splendensTV01 |--A. subg. DracunculusM79 | |--A. dracunculusM79 | |--A. filifoliaM79 | |--A. marschallianaTV01 | |--A. pedatifidaM79 | |--A. scopariaTV01 | `--A. spinescens [=Picrothamnus spinescens]M79 `--A. subg. SeriphidiumM79 |--A. sect. SeriphidiumTV01 | |--A. ciniformisTV01 | |--A. fragransTV01 | |--A. gypsaceaTV01 | `--A. kopetdaghensisTV01 `--A. sect. TridentataeM79 Artemisia incertae sedis: A. absinthiumC55 A. albaR-CT01 A. annuaH93 A. asiaticaS00 A. caerulencensM79 A. campestrisH93 |--A. c. ssp. campestrisH93 `--A. c. ssp. borealisH93 A. camphorataC90 A. canadensisJ23 A. capillarisO88 A. carruthiBT87 A. caruifoliaO88 A. caudataNC01 A. cernuaJ23 A. columbiensisJ23 A. douglasianaH93 A. gmeliniiO88 A. herba-albaL98 A. judaicaTV01 A. longifoliaJ23 A. lucenticaTV01 A. michauxianaH93 A. monospermaL98 A. nesiotica [incl. A. californica var. insulare]H93 A. nilagiricaD07 A. norvegicaH93 |--A. n. ssp. norvegicaH93 `--A. n. ssp. saxatilisH93 A. princepsMH98 A. pycnocephalaH93 A. reptansTV01 A. roxburghianaO88 |--A. r. var. roxburghianaO88 `--A. r. var. purpurascensO88 A. scopulorumGS99 A. serrataJ23 A. sieversianaO88 A. strictaO88 A. suksdorfiiH93 A. wallichianaO88
*Type species of generic name indicated
References
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