Othonna
Encyclopedia
Othonna is a genus
of evergreen or deciduous geophytes, dwarf succulents or shrub
s belonging to the sunflower family Asteraceae
. The genus includes more than 100 species
concentrated in the Western Cape of South Africa
and southern Namibia
. A few species occur in summer rainfall parts of southern Africa
. The genus is closely allied to Senecio
and can be distinguished principally by details of the involucre. Taxonomically
they are in need of a modern revision.
The form or habit of othonnas is very diverse and in this lies much of their appeal to collectors of winter growing succulent plants. The various species may be pachycauls with elongate but proportionately swollen stems, caudiciform caudiciforms
or dwarf and compact succulents with short branches. A highly distinctive group is made up tuberous geophytes with subterranean rootstocks and deciduous stems or leaves. Other species are orthodox shrubs.
Leaf diversity is also notable in this genus. A few species possess highly succulent leaves (e.g., O. capensis, O. sedifolia) but most have bifacial leaves that are only slightly succulent. Size and shape is variable, with most species having leaves in the 1-10 cm long range, common shapes being elliptic, lanceolate, oblanceolate or spathulate. The leaf blades may be intricately divided (O. abrotanifolia) or lobed (O. cakilaefolia), amplexicaul or distinctly undulate. Often the leaves are sessile and the lamina is glaucous; leaf margins are entire to coarsely toothed. Some species are dimorphic in that the acaulescent juvenile leaves are very different from the adult leaves that are produced on the flowering stems.
With few exceptions the flowers of othonnas fit the stereotypical "DYC" ("Damned Yellow Composite
", a tongue-in-cheek phrase used for a variety of composites) designation. A simple or branched inflorescence gives rise to daisy-like flower heads. The exceptions are a handful of attractive purple-flowered species that are deciduous geophytes. Most if not all species are self-incompatible. The seeds are often proportionately heavy and probably do not travel far from the parent plant without the assistance of brisk winds. In at least some cases the seeds exude a sticky substance when wetted and thus affix themselves to the soil surface, aiding in the establishment of seedlings.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of evergreen or deciduous geophytes, dwarf succulents or shrub
Shrub
A shrub or bush is distinguished from a tree by its multiple stems and shorter height, usually under 5–6 m tall. A large number of plants may become either shrubs or trees, depending on the growing conditions they experience...
s belonging to the sunflower family Asteraceae
Asteraceae
The Asteraceae or Compositae , is an exceedingly large and widespread family of vascular plants. The group has more than 22,750 currently accepted species, spread across 1620 genera and 12 subfamilies...
. The genus includes more than 100 species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
concentrated in the Western Cape of South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
and southern Namibia
Namibia
Namibia, officially the Republic of Namibia , is a country in southern Africa whose western border is the Atlantic Ocean. It shares land borders with Angola and Zambia to the north, Botswana to the east and South Africa to the south and east. It gained independence from South Africa on 21 March...
. A few species occur in summer rainfall parts of southern Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
. The genus is closely allied to Senecio
Senecio
Senecio is a genus of the daisy family that includes ragworts and groundsels. The flower heads are normally rayed, completely yellow, and the heads are borne in branched clusters...
and can be distinguished principally by details of the involucre. Taxonomically
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
they are in need of a modern revision.
The form or habit of othonnas is very diverse and in this lies much of their appeal to collectors of winter growing succulent plants. The various species may be pachycauls with elongate but proportionately swollen stems, caudiciform caudiciforms
Caudex
A caudex is a form of stem morphology appearing as a thickened, short, perennial stem that is either underground or near ground level . It may be swollen for the purpose of water storage, especially in xerophytes...
or dwarf and compact succulents with short branches. A highly distinctive group is made up tuberous geophytes with subterranean rootstocks and deciduous stems or leaves. Other species are orthodox shrubs.
Leaf diversity is also notable in this genus. A few species possess highly succulent leaves (e.g., O. capensis, O. sedifolia) but most have bifacial leaves that are only slightly succulent. Size and shape is variable, with most species having leaves in the 1-10 cm long range, common shapes being elliptic, lanceolate, oblanceolate or spathulate. The leaf blades may be intricately divided (O. abrotanifolia) or lobed (O. cakilaefolia), amplexicaul or distinctly undulate. Often the leaves are sessile and the lamina is glaucous; leaf margins are entire to coarsely toothed. Some species are dimorphic in that the acaulescent juvenile leaves are very different from the adult leaves that are produced on the flowering stems.
With few exceptions the flowers of othonnas fit the stereotypical "DYC" ("Damned Yellow Composite
Damned yellow composite
A damned or damn yellow composite is a jocular reference to the difficulty of distinguishing many of the numerous species of composite that have yellow flowers and can be difficult to tell apart in the field. It is sometimes reserved for those yellow composites of no particular interest...
", a tongue-in-cheek phrase used for a variety of composites) designation. A simple or branched inflorescence gives rise to daisy-like flower heads. The exceptions are a handful of attractive purple-flowered species that are deciduous geophytes. Most if not all species are self-incompatible. The seeds are often proportionately heavy and probably do not travel far from the parent plant without the assistance of brisk winds. In at least some cases the seeds exude a sticky substance when wetted and thus affix themselves to the soil surface, aiding in the establishment of seedlings.
Selected species
- Othonna arminiana
- Othonna cacalioides
- Othonna capensisOthonna capensisOthonna capensis also known as Little Pickles, is a species of the genus Othonna and family Asteraceae and is a native of South Africa....
- Othonna cinerariaJacobaea maritimaJacobaea maritima is a perennial plant species in the genus Jacobaea in the family Asteraceae, native to the Mediterranean region...
- Senecio cineraria
- Cineraria maritima
- Jacobaea maritima
- Othonna clavifoliaOthonna clavifoliaOthonna clavifolia is a species of flowering plant in the Asteraceae family.It is found only in Namibia.Its natural habitat is rocky areas.It is threatened by habitat loss.-References:* Craven, P. 2004. . Downloaded on 20 July 2007....
- Othonna euphorbioides
- Othonna furcata
- Othonna geifolia L.
- Cineraria geifolia (L.) L.
- Othonna coronopifolia L.
- Othonna hederifolia
- Othonna herrei
- Othonna lepidocaulis
- Othonna retrofracta
- Othonna palustrisSenecio congestusSenecio congestus, also known by its common names Swamp Ragwort, Northern Swamp Groundsel, Marsh Fleabane, Marsh Fleawort, Clustered Marsh Ragwort and Mastodon Flower, a herbaceous member of the Asteraceae family and the Senecio genus, can be seen most easily when its bright yellow umbel flowers...
- Senecio congestus
- Tephroseris palustris
- Othonna wrinkleana
External links
- Othonna 1998-2004 Philippe Faucon. Retrieved on February 5, 2007.
- African succulents 2003 African Succulents. Retrieved on February 5, 2007.