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Dendrosenecio
Dendrosenecio kilimanjari
Scientific classification
Kingdom:	Plantae
Division:	Magnoliophyta
Class:	Magnoliopsida
Subclass:	Asteridae
(unranked):	Euasterids II
Order:	Asterales
Family:	Asteraceae
Subfamily:	Asteroideae
Tribe:	Senecioneae
Genus:	Dendrosenecio (Hauman ex Hedberg) B. Nord.
Species
D. adnivalis D. battiscombei D. cheranganiensis D. elgonensis D. erici-rosenii D. johnstonii D. keniensis D. keniodendron D. kilimanjari D. meruensis D. brassicaformis
Range of Dendrosenecio
Synonyms
Senecio L.

Dendrosenecio originally listed as the genus Senecio, always a member of the family Asteraceae, are the Giant groundsel or "giant cabbage trees" endemic to the tall, equatorial mountains of eastern Africa.

Nomen confusum

Studies of the giant Senecio of Africa suffered from an unfortunate mix-up in some of the samples that were collected in 1922. The collected materials united the leaf of Lobelia gregoriana with the inflorescence of S. keniensis and the other way around also. This confusion of materials crossed samples between not just genus but also families as Lobelia is of the family Campanulaceae and Senecio is of the family Asteraceae. At that time, Senecio keniensis was rejected as a confused name (nomen confusum) based on the muddled samples from which made it impossible to select a single specimen, but that practice is no longer permitted and the replacement name S. brassica is superfluous and other names that were based on this basionym are similarly illogical and incorrectly deduced. Examples: Fries and Fries (1922) cited the confused material for S. brassica; Hedberg (1957) selected a single specimen from among the syntypes that associated S. brassica with Fries & Fries (1305). The first mention of genus name Dendrosenecio seems to have come from Lucien Leon Hauman in 1935.

Terminal taxa

• Dendrosenecio adnivalis (Stapf) E.B.Knox (1993)
• Dendrosenecio battiscombei (R.E.Fr. & T.C.E.Fr.) E.B.Knox (1993)
• Dendrosenecio brassica (R.E.Fr. & T.C.E.Fr.) B.Nord. (1978)
• Dendrosenecio brassiciformis (R.E.Fr. & T.C.E.Fr.) Mabb. (1986)
• Dendrosenecio cheranganiensis (Cotton & Blakelock) E.B.Knox (1993)
• Dendrosenecio elgonensis (T.C.E.Fr.) E.B.Knox (1993)
• Dendrosenecio erici-rosenii (R.E.Fr. & T.C.E.Fr.) E.B.Knox (1993)
• Dendrosenecio johnstonii (Oliv.) B.Nord. (1978)
• Dendrosenecio keniensis (Baker f.) Mabb. (1986)
• Dendrosenecio keniodendron (R.E.Fr. & T.C.E.Fr.) B.Nord. (1978)
• Dendrosenecio kilimanjari (Mildbr.) E.B.Knox (1993)
• Dendrosenecio meruensis (Cotton & Blakelock) E.B.Knox (1993)

Distribution

The mountains in Africa have slopes with vertical gradients of precipitation and temperature fluctuations; the tallest of the African mountains are located at and near the equator which limits the gradient of environmental fluctuations to daily events, warm days and cold nights consistent throughout the year. Of the many mountain ranges in Africa, only a few clearly reach above the treeline and of those few, Mount Kilimanjaro (5,985 metres (19,636 ft)), Mount Kenya (5,198 metres (17,054 ft)) and Ruwenzori 5,109 metres (16,762 ft)). Mount Kenya is alone where it is, but Mount Kilimanjaro and the Ruwenzori both have relatively tall neighboring mountains that support similar flora.

3400-3800 meters (11,000-12,000 feet)

Given the name Afro-alpine region by Hauman in 1955. There is a sharp boundry at 3400 meters (3000 meters on the North side) that separates the forest from the lower alpine zone, the environment is a moorland (low growing vegetationon acidic soils) and it is here that the Dendrosenecio start to grow among the mountain tussocks and sedges.

Dendrosenecio brassica grows in this region on Mount Kenya. Dendrosenecio johnstonii on all three of the tallest mountains.

3800-4500 meters (12,000-15,000 ft)

The upper moorlands; this is where most of the D. brassica make their homes on all three of the mountains, living with tough dwarf shrubs.

4300-5000 meters (14,000-16,000 ft)

Dendrosenecio woodlands, where each mountain has its own special variety. Dendrosenecio keniensis on Mount Kenya, Dendrosenecio kilimanjari on Mount Kilimanjari and other species each on their own mountain.

4500 meters-peak (15,000 ft)

Populations of Dendrosenecio start to dwindle. Mount Kenya has the least vegetation in its upper parts due to its freezing temperatures.

Dispersal and establishment

Little variation was found in molecular phylogeny among the 40 recorded giant senecio collections (40 assessions), yet as a group they differ significantly from Cineraria deltoidea, the closest known relative. Biogeographic interpretation of the molecular phylogeny suggests that in the most recent one million years, the first giant senecios established themselves at higher elevations of Mount Kilimanjaro and became the species D. kilimanjari. As they moved down that mountain, adapting to live in the different environment at the lower altitudes of Mount Kilimanjaro, they became a new species, D. johnstonii. Some seeds found a way to Mount Meru and established themselves as the species D. meruensis, others found a way to get from Mount Kilamanjaro to the Aberdare Range and established themselves as D. battiscombei. D. battiscombei migrated into the wet alpine habitat on the Aberdares resulted in the formation of the species D. brassicaformis. Dispersal from the Aberdares to Mount Kenya established a second isolated population of D. battiscombei. Altitudinal speciation on Mount Kenya resulted in the formation of D. keniodendron and the "dwarf" D. keniensis. Dispersal from Mount Kenya back to the Aberdares established a second insular population of D. keniodendron. Dispersal from the Aberdares to the Cherangani Hills established two subspecies of D. cheranganiensis: D. cheranganiensis subsp. cheranganiensis and altitudinal (sub)speciation into the web alpine habitat resulted in D. cheranganiensis subsp. dalei. Dispersal from the Aberdares to Mount Elgon established D. elgonensis which is a point where several subspecies diverge and disperse: from Mount Elgon to the Virunga Mountains established D. erici-rosenii; from Mount Elgon to Mount Kahuzi (Mitumba Mountains) established a second population of D. erici-rosenii and dispersal from the Virunga Mountains to the Ruwenzori Range established a third population.

Gridded Adaptive Speciation Studies

Groundsels of several species are found throughout the world as common roadside weeds, but nowhere except in the highlands of Africa do they exhibit such large tree forms.

The mountains of central and eastern Africa are a model system for studying speciation and adaptation in plants. These mountains are predominantly volcanic peaks which rise far above the surrounding plains and plateaus, forming "islands in the sky"; tall enough be easily conceptualized as an array of isolated habitats easily described for biogeographic analysis; their age and arrangement around the Lake Victoria basin allow the disentanglement of the effects of time and position. The distances between the mountains range from 50 kilometres (31 mi) to 1,000 kilometres (620 mi) around the equator which minimizes the climatic differences making one stable dimension for the grid, location by altitude the other dimension. The alpine zone was described by Karl Olov Hedberg as having "summer every day, winter every night" because the daily temperature fluctuation vastly exceeds the yearly variation in average daily temperature. This unusual climate has important consequences for plant water-relations, photosynthesis, and growth and development.

The communities of giant senecio and giant lobelias found on these African mountains are an exceptional example of parallel or convergent evolution and repeated convergent evolution between these two groups; providing evidence that the unusual features of these plants are an evolutionary response to a challenging environment.

In the alpine zone the most extreme examples of the giant-rosette growth form are found, with adaptations that include:

• Massive leaf rosettes in which leaf development occurs in a large "apical bud"
• Water storage in the pith of the stem
• Insulation of the stem by retaining withered and dead foliage
• Secretion and impoundment of ice-nucleating polysaccharide fluids (a natural anti-freeze)
• Nyctinastic leaf movement (the leaves close when it gets cold)

At lower altitudes the daily temperature fluctuations are less extreme, the average daily temperature steadily increases, and the growth forms and ecology of the giant senecios and giant lobelias reflect the increased influence of biotic factors (such as competition for light) over abiotic factors (such as nightly frost).

Cytological Uniformity

The gametophytic chromosome number (is the number of chromosomes in each cell) for the giant Dendrosenecio is n = 50, and for the giant lobelias (specifically Lobeliaceae, Lobelia subgenus Tupa section Rhynchopetalum ) it is n = 14. Only five of the 11 species of giant senecio and three of the 21 species of giant lobelia from eastern Africa remain uncounted. Although both groups are polyploid, Dendrosenecio is presumed to be decaploid (ten sets; 10x) and the Lobelia more certainly tetraploid (four sets; 4x), their adaptive radiations involved no further change in chromosome number. The cytological uniformity within each group, while providing circumstantial evidence that they descended from a single ancestor and simplifying interpretations of cladistic analyses, provides neither positive nor negative support for a possible role of polyploidy in evolving the giant-rosette growth-form.

References

1. Germplasm Resources Information Network (GRIN) (2005-01-29). "Genus: Dendrosenecio (Hauman ex Hedberg) B. Nord" (HTML). Taxonomy for Plants. USDA, ARS, National Genetic Resources Program, National Germplasm Resources Laboratory, Beltsville, Maryland. Retrieved 2008-03-29.
2. ^ Cyrille Chatelain, Laurent Gautier, Raoul Palese. "Dendrosenecio (Hauman ex Hedberg) B.Nord" (HTML). African Flowering Plants Database. Conservatoire et Jardin botaniques de la Ville de Genève. Retrieved 2008-03-29.{{cite web}}: CS1 maint: multiple names: authors list (link)
3. ^ Aluka. "Entry for Dendrosenecio keniensis (Baker f.) Mabb" (HTML). African Plants. Ithaka Harbors, Inc. Retrieved 2008-03-28.
4. ^ Knox, Eric B. (1998). "Evolution of the giant senecios revisited; comparison of ITS and cpDNA phylogenetic estimates" (HTML). American Society of Plant Taxonomists Abstract Index. Department of Biological Sciences, Rutgers University. Retrieved 2008-03-29. {{cite journal}}: More than one of |work= and |journal= specified (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
5. Aluka. "Isotype of Senecio keniensis Baker" (HTML). African Plants. Ithaka Harbors, Inc. Retrieved 2008-03-29.
6. Natural Resources Conservation Service (NRCS). "Frequently Asked Questions -- definition for nomen confusum" (HTML). The PLANTS Database. United States Department of Agriculture,. Retrieved 2008-03-28. nomen confusum (Latin): confused name. Based on heterogenous elements from which it is impossible to select a lectotype.{{cite web}}: CS1 maint: extra punctuation (link)
7. Aluka. "Entry for Dendrosenecio keniensis (Baker f.) Mabb" (HTML). African Plants. Ithaka Harbors, Inc. Retrieved 2008-03-30.
8. Hedberg, Olov (12 April 1969). "Growth Rate of the East African Giant Senecios". Nature (222): 163–164. doi:10.1038/222163a0. Retrieved 2008-03-29. The most conspicuous plants of the alpine belt on the high East African mountains are a group of peculiar giant groundsels, characterized by sparsely sympodially branched woody stems crowned by huge leaf rosettes, each of which finally produces a large terminal inflorescence. These plants deviate so much from ordinary senecios that they have been allotted a separate subgenus, Dendrosenecio.
9. Weischet, Wolfgang (2000). Regionale Klimatologie Teil 2 Die Alte Welt: Europa - Afrika - Asien (Regional climatology, Part 2: The old world: Europe - Africa - Asia). p. 625. ISBN 9783443071196. {{cite book}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
10. Hauman, L. L. (1955). "La "region afroapline" en phytogeographie centro africaine". Webbia XI: 467–489.
11. Bussmann, Fainer W. (June 2006). "Vegetation zonation and nomenclature of African Mountains - An overview". Lyonia. Retrieved 2008-04-27.
12. Hedberg, Olov (1951). "Vegetation belts of the East -African mountains". Svensk Botanisk Tidskrift. 45: 141–196.
13. Hedberg, Olov (1955). "Vegetation belts of the East -African mountains". Proceedings of the Linnean Society of London (Botany). 165: 134–136.
14. Aluka. "Cineraria deltoidea Sond" (HTML). African Plants. Ithaka Harbors, Inc. Retrieved 2008-03-30.
15. Knox, Eric B. (October 24, 1995). "Chloroplast DNA Variation and the Recent Radiation of the Giant Senecios (Asteraceae) on the Tall Mountains of Eastern Africa". Proceedings of the National Academy of Sciences of the United States of America. 92 (22). National Academy of Sciences: pp. 10349-10353. Retrieved 2008-03-29. {{cite journal}}: |pages= has extra text (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
16. ^ Knox, Eric B. (2004). "Adaptive radiation of African montane plants". In Ulf Dieckmann (ed.). Adaptive Speciation (HTML). Cambridge University Press. pp. 476 pages. ISBN 0521828422. Retrieved 2008-03-29. {{cite book}}: External link in |chapterurl= (help); Unknown parameter |chapterurl= ignored (|chapter-url= suggested) (help)
17. Roosevelt, Theodore (2007-09-18). "LOGICALLY". Life-histories of African Game Animals (HTML) (1 ed.). C. Scribner's Sons. Retrieved 2008-03-28. Groundsels of several species are found throughout the world as common roadside weeds, but nowhere except in the highlands of Africa do they exhibit such large tree forms. {{cite book}}: External link in |chapterurl= (help); Unknown parameter |chapterurl= ignored (|chapter-url= suggested) (help); Unknown parameter |coauthors= ignored (|author= suggested) (help); Unknown parameter |origdate= ignored (|orig-date= suggested) (help)
18. Aluka. "Isotype of Tupa rhynchopetalum (A. Rich.) Hochst" (HTML). African Plants. Ithaka Harbors, Inc. Retrieved 2008-03-30.
19. Knox, Eric B. (July 1993). "Chromosome Numbers of the East African Giant Senecios and Giant Lobelias and their Evolutionary Significance". American Journal of Botany. 80 (7). Botanical Society of America: pp. 847-853. doi:10.2307/2445604. Retrieved 2008-03-29. {{cite journal}}: |pages= has extra text (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)

External links

Media related to Dendrosenecio at Wikimedia Commons

• Dendrosenecio
• Asteraceae