''Didelta'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of shrubs of up to 1 or 2 meter high, with two known species in the

daisy family The family Asteraceae, alternatively Compositae, consists of over 32,000 known species of flowering plants in over 1,900 genera within the order Asterales. Commonly referred to as the aster, daisy, composite, or sunflower family, Compositae w ...

. Like in almost all Asteraceae, the individual flowers are

5-merous Merosity (from the greek "méros," which means "having parts") refers to the number of component parts in a distinct whorl of a plant structure. The term is most commonly used in the context of a flower where it refers to the number of sepals in a w ...

, small and clustered in typical heads, and are surrounded by an

involucre In botany, a bract is a modified or specialized leaf, especially one associated with a reproductive structure such as a flower, inflorescence axis or cone scale. Bracts are usually different from foliage leaves. They may be smaller, larger, or of ...

, consisting of in this case two

whorls A whorl ( or ) is an individual circle, oval, volution or equivalent in a whorled pattern, which consists of a spiral or multiple concentric objects (including circles, ovals and arcs). Whorls in nature File:Photograph and axial plane floral ...

of bracts, which are almost free from each other. The 3–5 outer bracts are protruding and triangular in shape, the inner about twice as many are lance-shaped and ascending. In ''Didelta'', the centre of the head is taken by 3–5 clusters of bisexual yolk yellow

disc florets Disk or disc may refer to: * Disk (mathematics), a geometric shape * Disk storage Music * Disc (band), an American experimental music band * ''Disk'' (album), a 1995 EP by Moby Other uses * Disk (functional analysis), a subset of a vector spac ...

, sometimes divided from each other by male disc florets, and is surrounded by one complete whorl of infertile yolk yellow

ray florets The family Asteraceae, alternatively Compositae, consists of over 32,000 known species of flowering plants in over 1,900 genera within the order Asterales. Commonly referred to as the aster, daisy, composite, or sunflower family, Compositae w ...

. The common base of the flowerhead swells around the developing fruitlets, become woody and breaks into segments when ripe. The fruitlets germinate within this woody encasing. The species of the genus ''Didelta'' can be found in Namibia and South Africa. The genus is called salad thistle in English and slaaibos in

Afrikaans Afrikaans (, ) is a West Germanic language that evolved in the Dutch Cape Colony from the Dutch vernacular of Holland proper (i.e., the Hollandic dialect) used by Dutch, French, and German settlers and their enslaved people. Afrikaans gra ...

Description

The species assigned to the genus ''Didelta'' are more or less

succulent In botany, succulent plants, also known as succulents, are plants with parts that are thickened, fleshy, and engorged, usually to retain water in arid climates or soil conditions. The word ''succulent'' comes from the Latin word ''sucus'', meani ...

shrub A shrub (often also called a bush) is a small-to-medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from trees ...

s or

perennial plant A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' -ennial'', "through the years") is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also wide ...

s, with or without milk sap, that can have both alternate and opposite leaves, that may be felty hairy or hairless, may have a spiny tip, are seated and have an entire, sometimes spiny margin. The flowerheads sit individually in the

leaf axil A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, ste ...

s or on a peduncle. These heads are subtended by 2 rows of free

involucral bract In botany, a bract is a modified or specialized leaf, especially one associated with a reproductive structure such as a flower, inflorescence axis or cone scale. Bracts are usually different from foliage leaves. They may be smaller, larger, or of ...

s, the outer 3–5 are protruding, triangular in shape, broadest and leaflike, the inner lance-shaped, ascending and may be spiny. Each head consists of a whorl of yellow, infertile ray florets with 4 teeth at their tips, surrounding yellow disc florets that each have five long, free lobes. Adjacent each of the outer involucral bracts, several florets are fertile, and the surrounding parts of the common base of all florets in the head (or receptacle) swell and eventually become woody. The receptacle breaks up at maturity, each section corresponding with one of the persistent outer bracts. These segments break free from the parent plant and act as the dispersal units. The ribbed, flask-shaped, more or less curved fruitlets germinate inside the protective encasement of the woody segments. These are topped by a pappus of winged scales that have merged at their base.

Differences between the species

'' D. spinosa'' lacks milk sap, has hairless, more or less oval leaves with spines that often enclose the stem at base, and the swollen, eventually woody segments of the receptacle containing the fruitlets lack spines. '' D. carnosa'' has milk sap, elliptic to linear, variably tomentose leaves, and the swollen and eventually woody segments of the receptacle containing the fruitlets are spiny. Two varieties are distinguished. ''D. carnosa'' var. ''carnosa'' is hairless or becomes hairless with age, while ''D. carnosa'' var. ''tomentosa'' remains densely felty hairy at least on the undersides of the leaves.

Differences with related genera

Cuspidia cernua ''Cuspidia'' is a genus of flowering plants in the daisy family.fruitlets and the fruiting head remains intact, while both ''Didelta''-species have chaffy pappus and the fruiting head breaks into several triangular segments when ripe.

Taxonomy

The first to describe species that are nowadays included in the genus ''Didelta'' was

Carl Linnaeus the Younger Carl Linnaeus the Younger, Carolus Linnaeus the Younger, Carl von Linné den yngre (Swedish; abbreviated Carl von Linné d. y.), or ''Linnaeus filius'' (Latin for ''Linnaeus the son''; abbreviated L.fil. (outdated) or L.f. (modern) as a botanic ...

in 1781 and he named them ''Polymnia carnosa'' and ''Polymnia spinosa''. The type species of that genus is ''

Polymnia canadensis ''Polymnia canadensis'', commonly known as whiteflower leafcup, is a flowering perennial plant in the family Asteraceae. It is native to eastern North America from Ontario south to Alabama and from Kansas, Oklahoma, and Minnesota east to North Ca ...

'', named by his father

Carl Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...

in 1758. '' Polymnia'' is however a rather unrelated plant from North America in the

Heliantheae The Heliantheae (sometimes called the sunflower tribe) are the third-largest tribe in the sunflower family (Asteraceae). With some 190 genera and nearly 2500 recognized species, only the tribes Senecioneae and Astereae are larger. The name is de ...

tribe The term tribe is used in many different contexts to refer to a category of human social group. The predominant worldwide usage of the term in English language, English is in the discipline of anthropology. This definition is contested, in p ...

, with which it shares broad outer involucral bracts. The French naturalist Pierre-Joseph Buc'hoz described in 1785 ''Breteuillia trianensis'', based on a plant that was growing in the botanical garden at the

Palace of Versailles The Palace of Versailles ( ; french: Château de Versailles ) is a former royal residence built by King Louis XIV located in Versailles, Yvelines, Versailles, about west of Paris, France. The palace is owned by the French Republic and since 19 ...

. In 1786, Charles L'Héritier described ''Didelta tetragoniifolia'', based on the same plant from Versailles. In his

Hortus Kewensis ''Hortus Kewensis, or a Catalogue of the Plants Cultivated in the Royal Botanic Garden at Kew'' by William Aiton was a 1789 catalogue of all the plant species then in cultivation at the Royal Botanic Gardens, Kew Royal Botanic Gardens, Kew is ...

published in 1789, the Scottish botanist

William Aiton William Aiton (17312 February 1793) was a Scotland, Scottish botanist. Aiton was born near Hamilton, Scotland, Hamilton. Having been regularly trained to the profession of a gardener, he travelled to London in 1754, and became assistant to Phi ...

reassigned ''P. carnosa'' and ''P. spinosa'' to

Carl Peter Thunberg Carl Peter Thunberg, also known as Karl Peter von Thunberg, Carl Pehr Thunberg, or Carl Per Thunberg (11 November 1743 – 8 August 1828), was a Swedish naturalist and an "apostle" of Carl Linnaeus. After studying under Linnaeus at Uppsala Un ...

's genus ''Choristea''.

Joseph Gaertner Joseph Gaertner (12 March 1732 – 14 July 1791) was a German botanist, best known for his work on seeds, ''De Fructibus et Seminibus Plantarum'' (1788-1792). Biography He was born in Calw, and studied in Göttingen under Albrecht von Haller. ...

created in 1791 the new genus ''Favonia'' for ''P. spinosa''.

Friedrich Wilhelm Klatt Friedrich Wilhelm Klatt (13 February 1825 Hamburg – 3 March 1897 Hamburg) was a German botanist who specialised in the study of African plants. As a child he showed artistic talent, but for financial reasons, training and a career in art cou ...

redescribed ''Polymnia carnosa'' in 1886 and named it ''Distegia acida''. These generic names have been regarded as

synonyms A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...

by most later botanists. Although ''Breteuillia'' is an earlier and validly described name, it was ignored by later botanist, and therefore it was suppressed in favour of ''Didelta''. ; SpeciesThe Plant List, search for Didelta
/ref> * ''

Didelta carnosa ''Didelta'' is a genus of shrubs of up to 1 or 2 meter high, with two known species in the daisy family. Like in almost all Asteraceae, the individual flowers are 5-merous, small and clustered in typical heads, and are surrounded by an involucre ...

'' (L.f.) Aiton -

Cape Province The Province of the Cape of Good Hope ( af, Provinsie Kaap die Goeie Hoop), commonly referred to as the Cape Province ( af, Kaapprovinsie) and colloquially as The Cape ( af, Die Kaap), was a province in the Union of South Africa and subsequen ...

Namibia Namibia (, ), officially the Republic of Namibia, is a country in Southern Africa. Its western border is the Atlantic Ocean. It shares land borders with Zambia and Angola to the north, Botswana to the east and South Africa to the south and ea ...

* ''

Didelta spinosa ''Didelta spinosa '' (L.f.) Aiton, belonging to the family of Asteraceae, is a Southern African woody shrub or small tree endemic to the West Coast and found from Saldanha Bay in the south across the Gariep into the south-west corner of Namib ...

'' (L.f.) Aiton -

Phylogeny

Based on DNA-analysis, ''Didelta'' belongs to the

subtribe Subtribe is a taxonomic category ranking which is below the rank of tribe and above genus. The standard suffix for a subtribe is -ina (in animals) or -inae (in plants Plants are predominantly photosynthetic eukaryotes of the kingdom Plant ...

Gorteriinae. This analysis suggests that ''Didelta'' is most related to '' Berkheya spinosissima'', with which it shares the dimorph involucral bracts. According to this study, the relationships within the Gorteriinae are as expressed in the following tree.

Reassigned species

The species that were originally described as, or moved to ''Didelta'', which since have been reassigned include the following: * ''Didelta cernua'' = ''Cuspidia cernua'' * ''Didelta annua'' = ''Cuspidia cernua''

Distribution

The species of the genus ''Didelta'' occur in southern Namibia and the western parts of the Northern and Western Cape provinces of South Africa.

References

{{Taxonbar, from=Q16295185 Arctotideae Asteraceae genera Flora of Southern Africa