Dendrosenecio johnstonii
Encyclopedia
Dendrosenecio johnstonii, formerly Senecio johnstonii, is a giant groundsel found in the middle altitudes of Mount Kilimanjaro
in Africa
. A recent botanical reclassification split off some species formerly in Senecio, putting the giant groundsels in the new genus Dendrosenecio. It also redefined the former species Senecio cottonii, as a subspecies of Dendrosenecio johnstonii. Both genera are in the family Asteraceae
. The giant grounsels of the genus Dendrosenecio evolved, about a million years ago, from a Senecio that established itself on Mount Kilimanjaro, with those that survived adapting into Dendrosenecio kilimanjari
. As it moved down the mountain, the adaptation
s necessary for the new environment created the new species, Dendrosenecio johnstonii. Various subspecies are found on other mountains
. It branches repeatedly, forming a dense canopy with 50 to 80 branches when mature. The leaves are hairless, heart-shaped (cordate) and large, 53 centimetres (approximately 2 feet) long by 40 centimetres (16 inches) wide.
The flower shoot is a tall, broad cone, 60 centimetres (about 2 feet) tall, and 40 centimetres (16 inches) wide, with the flower heads horizontal. Each floret is about 25 millimetres (one inch) long, and the compound flower is made up of 11 to 15 of the petal-like ray florets, with thirty to fifty "disc" florets in the centre.
The following excerpts were presented as first hand accounts:
Kilimanjaro (1903): "Ravines longer retain a somewhat richer vegetation. The last stunted Erica
-trees disappear from them at 2,900 meters; and are replaced by a new characteristic plant of very peculiar habit, the arboreous Senecio johnstonii, with a spongy, simple or forked stem, the top of which bears a rosette of leaves as long as one's arm, and a dense inflorescence a meter in length."
Kilimanjaro (2007): "There is no bamboo zone, nor a Hagenia
-Hypericum
zone. Above about 4,600 meters, very few plants are able to survive the severe conditions, although specimens of Helichrysum newii have been recorded as high as 5,760 meters (close to a fumarole
), and moss
es and lichen
s are found right up to the summit. The upland moor
consists primarily of heath
/scrub plants, with Erica excelsa (Erica rossii), Philippia trimera (Erica trimera), Adenocarpus mannii, Protea kilimandscharica (Protea caffra
), Stoebe kilimandscharica (Seriphium kilimandscharicum), Myrica meyeri-johannis (Morella salicifolia), and Myrsine africana
. Grasses are abundant in places, and Cyperaceae
form the dominant ground cover in wet hollows. On flatter areas between the upland moor and the forest edge are areas of moorland or upland grassland
composed of Agrostis producta, Festuca convoluta (Poa kilimanjarica), Koeleria gracilis (Koeleria capensis), Deschampsia
sp., Exotheca abyssinica and Andropogon amethystinus, with scattered bushes of Adenocarpus mannii, Kotschya recurvifolia and Myrica meyeri-johannis (Morella salicifolia). Various species of Helichrysum are found in the grasslands and in the upland moor. Two distinct forms of giant groundsel occur on the upper mountain: Senecio johnstonii cottonii, endemic to the mountain and only occurring above 3600 meters , and S.johnstonii johnstonii which occurs between 2,450 meters and 4,000 meters, and shows two distinct forms. At all altitudes Senecio favours the damper and more sheltered locations, and in the alpine bog
s is associated with another conspicuous plant, growing up to 10m tall, the endemic giant lobelia Lobelia deckenii
. Below the tree line, the park
includes six corridors through the forest to the mountain foot."
Mount Kilimanjaro
Kilimanjaro, with its three volcanic cones, Kibo, Mawenzi, and Shira, is a dormant volcano in Kilimanjaro National Park, Tanzania and the highest mountain in Africa at above sea level .-Geology:...
in 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...
. A recent botanical reclassification split off some species formerly in Senecio, putting the giant groundsels in the new genus Dendrosenecio. It also redefined the former species Senecio cottonii, as a subspecies of Dendrosenecio johnstonii. Both genera are in the 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 giant grounsels of the genus Dendrosenecio evolved, about a million years ago, from a Senecio that established itself on Mount Kilimanjaro, with those that survived adapting into Dendrosenecio kilimanjari
Dendrosenecio kilimanjari
Dendrosenecio kilimanjari is a giant groundsel found atop Mount Kilimanjaro in Africa. It was originally known as Senecio kilimanjari, but a recent botanical reclassification split off some species formerly in Senecio, putting it and various other species in the new genus Dendrosenecio. Both genera...
. As it moved down the mountain, the adaptation
Adaptation
An adaptation in biology is a trait with a current functional role in the life history of an organism that is maintained and evolved by means of natural selection. An adaptation refers to both the current state of being adapted and to the dynamic evolutionary process that leads to the adaptation....
s necessary for the new environment created the new species, Dendrosenecio johnstonii. Various subspecies are found on other mountains
Description
Dendrosenecio johnstonii can be up to 10 meters tall, and grow to 40 centimeters (17 inches) or more in diameter. The centre of the stem, at full size, contains 1 to 2 centimeters of pithPith
Pith, or medulla, is a tissue in the stems of vascular plants. Pith is composed of soft, spongy parenchyma cells, which store and transport nutrients throughout the plant. In eudicots, pith is located in the center of the stem. In monocots, it extends also into flowering stems and roots...
. It branches repeatedly, forming a dense canopy with 50 to 80 branches when mature. The leaves are hairless, heart-shaped (cordate) and large, 53 centimetres (approximately 2 feet) long by 40 centimetres (16 inches) wide.
The flower shoot is a tall, broad cone, 60 centimetres (about 2 feet) tall, and 40 centimetres (16 inches) wide, with the flower heads horizontal. Each floret is about 25 millimetres (one inch) long, and the compound flower is made up of 11 to 15 of the petal-like ray florets, with thirty to fifty "disc" florets in the centre.
Distribution
D. johnstonii lives between the altitudes of 2,750 and 3,350 meters (9,000 and 11,000 feet) on Kilimanjaro.The following excerpts were presented as first hand accounts:
Kilimanjaro (1903): "Ravines longer retain a somewhat richer vegetation. The last stunted Erica
Erica
Erica ,the heaths or heathers, is a genus of approximately 860 species of flowering plants in the family Ericaceae. The English common names "heath" and "heather" are shared by some closely related genera of similar appearance....
-trees disappear from them at 2,900 meters; and are replaced by a new characteristic plant of very peculiar habit, the arboreous Senecio johnstonii, with a spongy, simple or forked stem, the top of which bears a rosette of leaves as long as one's arm, and a dense inflorescence a meter in length."
- "Senecio johnstonii bears the least resemblance to the alpine habit in this region. It is remarkable, however, that plants of similar habit are also found on tropical high mountains elsewhere. For the VellozieaeVelloziaceaeVelloziaceae is a botanical name for a family of flowering plants. Such a family has been recognized by many taxonomists.The APG II system, of 2003 , also recognizes this family, and assigns it to the order Pandanales in the clade monocots...
of Brazil are similar, and so to some extent are species of EspeletiaEspeletiaEspeletia, commonly known as Frailejón or Fraylejón is a genus of perennial subshrubs, in the family Asteraceae. The genus, which is endemic mainly to Colombia, Venezuela and Ecuador, was first formally described by botanist Alexander Von Humboldt in 1801...
in the Cordilleras of VenezuelaCordillera de MéridaThe Cordillera de Mérida is a series of mountain ranges, or massif, in northwestern Venezuela. The Cordillera de Mérida is a northeastern extension of the Andes Mountains. The ranges run southwest–northeast between the Venezuelan–Colombian border and the Venezuelan coastal range...
.... In other respects the impress of the alpine climate is most clearly stamped on the vegetation, especially in the higher part of the region, with its dwarf plants. Protective measures against transpiration are everywhere strongly developed, in particular dense coatings of woolly hairs are frequent."
Kilimanjaro (2007): "There is no bamboo zone, nor a Hagenia
Hagenia
Hagenia abyssinica is a species of flowering plant native to the high-elevation Afromontane regions of central and eastern Africa. It also has a disjunct distribution in the high mountains of East Africa from Sudan and Ethiopia in the north, through Kenya, Uganda, Rwanda, Burundi, Democratic...
-Hypericum
Hypericum
Hypericum is a genus of about 400 species of flowering plants in the family Hypericaceae ....
zone. Above about 4,600 meters, very few plants are able to survive the severe conditions, although specimens of Helichrysum newii have been recorded as high as 5,760 meters (close to a fumarole
Fumarole
A fumarole is an opening in a planet's crust, often in the neighborhood of volcanoes, which emits steam and gases such as carbon dioxide, sulfur dioxide, hydrochloric acid, and hydrogen sulfide. The steam is created when superheated water turns to steam as its pressure drops when it emerges from...
), and moss
Moss
Mosses are small, soft plants that are typically 1–10 cm tall, though some species are much larger. They commonly grow close together in clumps or mats in damp or shady locations. They do not have flowers or seeds, and their simple leaves cover the thin wiry stems...
es and lichen
Lichen
Lichens are composite organisms consisting of a symbiotic organism composed of a fungus with a photosynthetic partner , usually either a green alga or cyanobacterium...
s are found right up to the summit. The upland moor
Moorland
Moorland or moor is a type of habitat, in the temperate grasslands, savannas, and shrublands biome, found in upland areas, characterised by low-growing vegetation on acidic soils and heavy fog...
consists primarily of heath
Heath (habitat)
A heath or heathland is a dwarf-shrub habitat found on mainly low quality acidic soils, characterised by open, low growing woody vegetation, often dominated by plants of the Ericaceae. There are some clear differences between heath and moorland...
/scrub plants, with Erica excelsa (Erica rossii), Philippia trimera (Erica trimera), Adenocarpus mannii, Protea kilimandscharica (Protea caffra
Protea caffra
Protea caffra is a small tree or shrub which occurs in open or wooded grassland usually on rocky ridges. Its leaves are leathery and hairless. The flower head is solitary or in clusters of 3 or 4 with the involucral bracts a pale red, pink or cream colour. The fruit is a densely hairy nut...
), Stoebe kilimandscharica (Seriphium kilimandscharicum), Myrica meyeri-johannis (Morella salicifolia), and Myrsine africana
Myrsine africana
Myrsine africana is a species of shrub in the Myrsinaceae family. It is indigenous to South Asia and Africa. It typically has dense, dark-green to red foliage and produces tiny bright purple berries.The shrub can achieve heights of over 2 meters and may be dense if pruned or grown in strong sunlight...
. Grasses are abundant in places, and Cyperaceae
Cyperaceae
Cyperaceae are a family of monocotyledonous graminoid flowering plants known as sedges, which superficially resemble grasses or rushes. The family is large, with some 5,500 species described in about 109 genera. These species are widely distributed, with the centers of diversity for the group...
form the dominant ground cover in wet hollows. On flatter areas between the upland moor and the forest edge are areas of moorland or upland grassland
Grassland
Grasslands are areas where the vegetation is dominated by grasses and other herbaceous plants . However, sedge and rush families can also be found. Grasslands occur naturally on all continents except Antarctica...
composed of Agrostis producta, Festuca convoluta (Poa kilimanjarica), Koeleria gracilis (Koeleria capensis), Deschampsia
Deschampsia
Deschampsia is a genus of grasses in the family Poaceae, commonly known as hair grass or tussock grass. There are 30 to 40 species....
sp., Exotheca abyssinica and Andropogon amethystinus, with scattered bushes of Adenocarpus mannii, Kotschya recurvifolia and Myrica meyeri-johannis (Morella salicifolia). Various species of Helichrysum are found in the grasslands and in the upland moor. Two distinct forms of giant groundsel occur on the upper mountain: Senecio johnstonii cottonii, endemic to the mountain and only occurring above 3600 meters , and S.johnstonii johnstonii which occurs between 2,450 meters and 4,000 meters, and shows two distinct forms. At all altitudes Senecio favours the damper and more sheltered locations, and in the alpine bog
Bog
A bog, quagmire or mire is a wetland that accumulates acidic peat, a deposit of dead plant material—often mosses or, in Arctic climates, lichens....
s is associated with another conspicuous plant, growing up to 10m tall, the endemic giant lobelia Lobelia deckenii
Lobelia deckenii
Lobelia deckenii is a species of giant lobelia of the mountains of East Africa. It grows in moist areas, such as valley bottoms and moorland, in contrast to Lobelia telekii which grows in a similar, but drier habitat. These two species produce occasional hybrids...
. Below the tree line, the park
Kilimanjaro National Park
Kilimanjaro National Park is a national park, located 200 miles south of the equater near Moshi, Tanzania. It is centered on Mount Kilimanjaro, and covers an area of from 2°45'–3°25'S, 37°00'–37°43'E....
includes six corridors through the forest to the mountain foot."