• Abstract and Figures
• Public Full-text

152 Plant Protection Quarterly Vol.21(4) 2006 on which the outer fl owers open fi rst and the inner ones do not develop fully. Fruits are grey-green pods 8–12 cm long. They are rounded at the base, but Review shortly pointed at the tip, similar to a man- go. Each fruit contains hundreds of seeds, which are brown, fl attened and have a tuft of long white hairs 2–3 cm long at one end. Seeds weigh 5.9–7 mg (Amritphale et al. 1984). The biology of Australian weeds The taproot grows up to 4 m long, with spreading lateral roots. Roots form large 45. Calotropis procera (Aiton) W.T.Aiton tubers with a starchy cortex that contains canals full of milky latex, giving roots a Blair S. Grace, Northern Territory Department of Natural Resources, spongy texture. Environment and the Arts, PO Box 30, Palmerston, NT 0831, Australia. Email: [email protected] Taxonomy The genus Calotropis contains three spe- cies, C. procera, C. gigantea (L.) W.T.Aiton and C. acia Buch.-Ham. (Rahman and Wilcock 1991). C. acia is not known to be Name Flowers are more or less tubular, fi ve present in Australia. C. gigantea is distin- The genus name Calotropis is derived from lobed, 2–3 cm across (Figure 1) without guished from C. procera mainly by having Greek calos (beautiful) and tropis (keel of milky sap. They are white with a deep pur- wider corollas and shorter sepals. Strains a boat), referring to scales in the fl owers ple blotch at the base of each lobe and deep of C. gigantea in Australia are sterile, and (Rahman and Wilcock 1991). The specifi c purple scales between the petals and the it is a garden plant that is capable of some name procera is derived from cera, Latin for stamens. Flowers are grouped in umbels limited spread by suckering from roots. wax, referring to the leaves (Parsons and Cuthbertson 2001). Commonly used synonyms for Calotro- pis procera (Aiton) W.T.Aiton (Asclepiad- aceae) include C. procera (L.) Dryand., C. procera (Aiton) R.Br., C. heterophylla Wall., C. busseana K.Schum, C. syriaca Woodson, C infl exa Chiov., Asclepias procera Aiton and incorrectly, C. procera (Willd.) R.Br. ex Ai- ton (Forster 1992). The common names rubber bush, rub- ber tree and Indian milkweed refer to the milky sap or latex produced in the stems and roots. Kapok refers to the fl uffy fi - bre attached to the seeds. Other common names used in Australia include king’s crown kapok, auricula tree, cabbage tree, King Edward’s crown, Prince of Wales’ crown and calotrope. Description Calotropis procera is a distinctive medium sized shrub or small tree up to 4 m high. Its stems are grey-green, smooth, rather crooked and older stems are covered with a soft, thick corky bark. The plant com- monly branches at the base. Stems exude copious quantities of sticky latex when damaged. Latex is produced by lactifer cells in the stems and roots (Ogundipe 1993). Leaves are large (5–20 cm long, 4–10 cm wide) and elliptic, rounded or ovate, grey-green in colour, with six prominent veins underneath. Leaves are thick in cross section, with a short pointed tip and a heart-shaped base that partly clasps the stem. Petioles are 3–4 mm long and 4–5 mm wide. A brush of hairs occurs at the Figure 1. Floral anatomy of Calotropis procera. Habit of fl owering branch base of the midvein. Each pair of opposite (A), apical view of fl ower (B), side view of fl ower with part of corolla leaves is at right angles to adjacent pairs. removed showing staminal column (C) and side view of staminal corona The plant is not deciduous. and staminal column (D). From Forster (1992) (reproduced with permission). Plant Protection Quarterly Vol.21(4) 2006 153 There are no known hybrids of C. of Queensland and the Northern Territory. procera in Australia. Two subspecies of C. The fact that C. procera is widespread in procera are recognized, but only one, C. tropical areas with over 1000 mm annual procera ssp. procera is naturalized in Aus- rainfall through to arid areas with rain- tralia (Forster 1992). There is considerable fall less that 200 mm suggests that it can polymorphism within C. procera in its na- tolerate a wide range of environmental tive range, but it is morphologically uni- conditions, hence it has a wide potential form in Australia, suggesting that Austral- distribution (Figure 3). ian populations have resulted from one or very few introductions (Forster 1992). Habitat Several authors claim that C. procera History is most common in overgrazed areas Calotropis procera was possibly introduced (Cheam 1984a,b,c, Barkhadle et al. 1994, into Australia through seeds in the pad- Parsons and Cuthbertson 2001, Smith ding in camel saddles, or as an ornamen- 2002), although it can also persist in oth- Figure 2. The distribution of tal plant during a gold rush in North er areas with high levels of disturbance, Calotropis procera in Australia. Queensland (Parsons and Cuthbertson such as coastal sand dunes (Anon. 2001), Data were taken from Forster (1992), 2001). It was fi rst recorded as naturalized watercourses and roadsides (Parsons Parsons and Cuthbertson (2001), around Chillagoe and Georgetown, North and Cuthbertson 2001). It can also form Navie (2004), Australia’s Virtual Queensland in 1935, but was present much dense thickets on alluvial fl ats (Parsons Herbarium (2005), Mark Gardener earlier (Parsons and Cuthbertson 2001). It and Cuthbertson 2001). Although dense (personal communication) and was fi rst observed in the Northern Terri- stands are common in disturbed or heav- Northern Territory Government tory in the Mataranka area, near Katherine ily grazed areas, C. procera is capable of in 1946–7. It spread along the Roper River establishing and persisting in areas with records. from there in the 1950s and the Victoria good pasture cover (Table 1). River, in north-western Northern Territory Most dense infestations occur on well in the 1960s. drained soil such as sandy levee soils along In Western Australia, a small patch near waterways rather than heavier clays (Ta- Kununurra was recorded in 1965, which ble 1). Plants growing in clay have stunted had expanded rapidly to 5000 ha by 1969, growth (Hall 1967). C. procera frequently and the plant now encompasses very large occurs around oases in arid parts of the areas of the Kimberley (Figure 2). Earlier Middle East (Willmer 1988) and is com- records of C. procera may exist in Western mon in boundaries between cultivated Australia, but it was confused with C. fi elds in northern Pakistan (Hussain et al. gigantea. C. procera was fi rst recorded in 2003). Its occurrence on coastal sand dunes northern South Australia in 1989. There is probably related to its ability to toler- is currently concern that it is spreading in ate high soil salinity (Parsons and Cuth- central Australia (Chris Brown personal bertson 2001). Its growth increases with communication). increasing nitrogen, but it is capable of Calotropis procera was introduced to surviving and reproducing in soils with north-eastern Brazil in the early 1900s (El- low nitrogen (Chadwick and Obeid 1963) Figure 3. The potential distribution lison and Barreto 2004). and it is clearly able to persist in very poor of Calotropis procera in Australia. soils in northern Australia. From Thorp and Lynch (2000) Distribution There were no gross morphological (reproduced with permission). Calotropis procera is native to tropical and differences observed between C. procera subtropical Africa and Asia but is more plants growing at low (0–300 m) and high common in the Middle East. It occurs in (1700–2000 m) altitudes (Alwadi and Ab- West Africa as far south as Angola, North ulfatih 1996). This suggests the plant is tol- Seedling growth is strongly affected and East Africa, Madagascar, the Arabian erant of temperatures ranging from frosts by allelochemicals from buffel grass Peninsula, southern and south-eastern to extreme desert heat. Young stems are (Cenchrus ciliaris L.), but seed germina- Asia, to Malaysia (Rahman and Wilcock surrounded by whitish fl uffy indumentum tion and seedling survival is unaffected 1991). The species is now naturalized in (Ogundipe 1993), which would provide (Cheam 1984a,b). Young stems contain Australia, Indonesia, many Pacifi c islands, protection from frost and desiccation. chlorophyll and become porous as they Mexico, Central and South America, the mature (Ogundipe 1993). Caribbean islands (USDA NRCS 2004, Growth and development Rahman and Wilcock 1991) and north- Little is known about the growth, develop- Reproduction eastern Brazil (Radunz 1983, Ellison and ment or phenology of C. procera in Aus- Calotropis procera is capable of producing Barreto 2004). tralian rangelands. In pot trials, seedlings large quantities of seeds. However, suck- In Australia, C. procera is widespread grew quite slowly initially, but growth ering from roots and crowns may be im- in the northern regions and is a problem rates increased after eight weeks (Table portant in the thickening of local patches in native pastures in drier monsoon ar- 2). Much of the early growth went into (Parsons and Cuthbertson 2001, Smith eas of tropical Australia (Martin 1996). It developing a strong root system (Cheam 2001). is found mostly in northern Queensland, 1984a,b). One mature plant from west- northern parts of the Northern Territory ern Northern Territory (2.4 m high, with Flowers and Western Australia (Figure 2). Infesta- stem diameters of 65, 120 and 190 mm) It is unknown at what age C. procera begins tions further south appear to be spreading; had above-ground portions that weighed to fl ower and seed, but Parsons and Cuth- these include patches in northern parts of 6.6 kg and below ground portions that bertson (2001) tentatively suggest that this South Australia and southern Northern weighed 2.2 kg (wet weights) (Stuart Wil- occurs once plants are two years old.

Load more

  9

Copy Link