Boneseed

Chrysanthemoides monilifera (also known as Boneseed or Bitou Bush in Australasia¹, or Bietou, Tick Berry, Bosluisbessie, or Weskusbietou in South Africa)² is an evergreen flowering shrub with glossy round leaves in the Asteraceae (daisy) family. It is native to South Africa and has become a major environmental weed in Australia and New Zealand.¹

Taxonomy

In Australia, C. m. ssp. monilifera is known by the common name 'Boneseed', while C. m. ssp. rotundata is known by the common name 'Bitou Bush'.⁴ In New Zealand subspecies are not distinguished and C. monilifera is simply known as 'Boneseed'.⁵

C. monilifera was first described by Carolus Linnaeus in 1754 under the name Osteospermum monilifera, however it was given its current binomial name in 1943 by T. Norlindh.²

The species name monilifera comes from the Latin, monile, meaning necklace or collar, referring to the shiny fruit arranged around the flowers like a necklace.²

Description

Boneseed is a perennial, woody, upright shrub, growing to 3 m (10 ft),⁶ although occasionally taller.¹ It is a member of the Asteraceae (daisy) family and has showy, bright yellow flowers in swirls of 5-8 'petals' (ray florets) up to 30 mm (1.4 in) in diameter.⁶ Fruit are berry-like, spherical at around 8mm in diameter, and turn dark-brown to black with a bone-coloured seed inside of 6-7 mm diameter. Leaves are 2-6 cm (0.8-2.4 in) long by 1.5-5 cm (0.6-2 in) wide, oval tapering to the base with irregularly toothed margins.¹

Bitou Bush can be distinguished from Boneseed in part due to its more rounded sprawling habit to 1.5-2 m (4.5-7 ft), less noticeably toothy leaf margins and seeds that are egg-like rather than spherical.⁷¹⁴⁶

Both Boneseed and Bitou Bush hybridise readily, however, so examples of plants demonstrating a fusion of traits is possible.¹

Distribution and habitat

Chrysanthemoides monilifera occurs naturally in coastal areas of South Africa, reaching into southern Namibia and Mozambique.³ The most widespread subspecies in South Africa is pisifera.³ Subspecies rotundata is concentrated along the eastern coast of South Africa from its southern tip through to the Mozambique border.³ Subspecies monilifera is concentrated around Cape Town and the Cape Peninsula on South Africa's south western coast.³

In Australia, subspecies rotundata (Bitou Bush) has naturalised along the coast of Queensland and New South Wales, while subspecies monilifera (Boneseed) has naturalised along and near the coast in parts of Victoria and South Australia.⁴

Introduction and spread in Australia

Boneseed was introduced to Australia as an ornamental garden plant from the mid-nineteenth century, with examples first recorded in gardens in Sydney in 1852 and Melbourne in 1858.⁴ It is thought that Boneseed had become naturalised in Australia, with self-sustaining populations, from around 1910.⁴ Bitou Bush arrived slightly later in around 1908, most likely in the ballast of a South African ship docked off New South Wales.⁸ Thereafter both subspecies were planted extensively to stabilise coastal sand dunes and control erosion, particularly from the mid-1940s to the 1960s, with Boneseed more commonly planted in Victoria and Bitou Bush more commonly planted in NSW and Southern Queensland.⁸ Boneseed was introduced to the You Yangs, south west of Melbourne, Victoria, to control soil erosion.⁴

By the late-1960s both species of C. monilifera had come to be recognised as significant weeds. Boneseed was proclaimed a noxious weed in Victoria in 1969.⁹ Not long thereafter, the Australian Institute of Agricultural Science (AIAS) suggested that Boneseed could potentially be "the most important weed on public land in southern Victoria" ¹⁰ due to its ability to colonise areas of bushland without the level of significant disturbance often required by other weedy species.¹⁰ In fact, the AIAS estimated that by 1976 Boneseed had colonised around 405 hectares in the You Yangs, with an even larger area affected on the Mornington Peninsula.¹⁰ Since then the population's expansion has been dramatic, and in the You Yangs, by 2003 it was estimated that Boneseed had extended its presence to around 1300 hectares of the 2000 hectare park.⁶

Australia recognised C. monilifera as a Weed of National Significance in 2000, meaning that it is considered to be one of the 20 most significant weeds in Australia today because of its invasiveness, potential for spread, and environmental and economic impacts.¹¹

C. monilifera has a particularly wide potential range.⁴ It is predicted that over time C. monilifera could significantly expand its current distribution to almost all of South Eastern Australia apart from the Alps.⁴

Impact

In Australia, Chrysanthemoides monilifera has been particularly successful in invading natural bushland. In part, this is due to the species' ability to establish on relatively nutrient-poor soils⁹ and in areas exposed to salt such as coastlines, as well as the ability of the seeds to germinate readily.⁶ Disturbances such as fire can assist C. monilifera to spread as the plant produces a large amount of seed that can persist in the soil seed bank for 10 years or more, and this reserve in turn enables the species to quickly recolonize a burnt area.¹

An individual plant can produce 50,000 seeds a year, about 60% of which are viable.⁶ Once germinated, seedlings grow vigorously with dense, bushy growth.⁹ This lush growth shades out and displaces slower growing native species that might otherwise occupy the same ecological niche.⁴ Rapid, vigorous growth also means that C. monilifera is capable of flowering and setting seed within 12-18 months,⁹ making it extremely persistent even in situations where disturbance or regular management activity is common.

Once established, the plant’s shallow root system enables it to absorb moisture after light rain before the moisture reaches the roots of more deeply rooted species⁶ further limiting opportunities for slower growing species to establish and out-compete C. monilifera over time. Furthermore, outside of Southern Africa the plant has few local, indigenous pathogens or predators to control its growth⁴ also reducing the potential for gaps to emerge that might provide opportunities for other species to restablish. The net consequence of C. monilifera's growth characteristics is that outside of its natural ecosystem it can ultimately form large, dense, unhealthy stands of a single species with extraordinarily poor biodiversity.

The plant can extend its existing range in a variety of ways. Its fruit is attractive to birds, rabbits, other animals and even some insects such as ants, and because seeds are tough and difficult to digest they will often be dispersed in animal droppings.¹²⁹ Seeds can also spread on vehicles and equipment, in contaminated soil, in garden waste, along water drainage lines and deliberately by human intervention.¹

C. monilifera, unlike many other weed species, is not generally considered to be a problem for agricultural productivity due to its sensitivity to trampling as well as being readily grazed by stock.⁶¹²⁹

Control

C. monilifera is potentially susceptible to a range of control strategies, however Burgman and Lindenmayer recommended that the strategy chosen be responsive to the local situation and available resources.⁴ Due to its relatively shallow root system removal by hand is an ideal method of control.⁴¹² Where manual removal is impractical many common herbicides can be used, in which case the herbicide is commonly applied directly to the wood of the plant via a cut notch or at the end of a pruned stump.⁴ Mechanical removal of C. monilifera by tractor or other machinery can also be effective, however this can be extremely indiscriminate and is only recommended in areas of poor environmental values and minimal erosion risk.⁴

Another method of control available is the use of controlled burns, however there are risks associated with this method. Principally, C. monilifera has higher moisture levels than many Australian indigenous species and therefore in Australia a higher than normal intensity fire is required for burns to be effective. This can in turn have detrimental impacts on indigenous vegetation evolved in response to more frequent, lower intensity fire. Furthermore, fire can trigger regermination from the extensive C. monilifera seed bank, potentially worsening the situation unless a program is implemented to monitor and control C. monilifera seedlings following the burn. If C. monilifera seedlings are removed, however, this can be extremely effective at exhausting the seed bank and minimising the chances of reinfestation.⁴⁶

Various methods of biological control have been attempted, particularly the introduction of insects adapted as natural enemies of C. monilifera such as the Bitou Tip Moth (Comostolopsis germana) and Bitou Seed Fly (Mesoclanis polana).⁴ In Australia, while these have had some success in controlling Bitou Bush (ssp. rotundata), to date they have not had similar success in combating Boneseed (ssp. monilifera).⁴

References

^ ^a ^b ^c ^d ^e ^f ^g ^h Blood, K (2001), Environmental weeds: a field guide for SE Australia, Melbourne, Vic., Australia: CH Jerram & Associates, p. 46-47, 86, ISBN 0957908601, OCLC 156877920
^ ^a ^b ^c van Jaarsveld, Ernst (April 2001), Chrysanthemoides monilifera (L.) T.Nord., Kirstenbosch, South Africa: SA National Biodiversity Institute, http://www.plantzafrica.com/plantcd/chrysanthmon.htm, retrieved on 2008-08-04 (Archived by WebCite)
^ ^a ^b ^c ^d ^e ^f Scott, John K (1996), "Population ecology of Chrysanthemoides monilifera in South Africa: implications for its control in Australia", The Journal of Applied Ecology 33 (6): 1496–1508, doi:10.2307/2404788, ISSN 0021-8901
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q Brougham, KJ; Cherry, H; Downey, PO (2006), Boneseed management manual: current management and control options for boneseed (Chrysanthemoides monilifera ssp. monilifera) in Australia, Sydney, NSW, Australia: Department of Environment and Conservation NSW, p. 2-5, http://www.weeds.org.au/WoNS/bitoubush/, retrieved on 2008-08-04 (Archived by the Wayback Machine: Introduction, Sections 1, 2, 3, 4, 5, 6)
^ ^a ^b Roy, Bruce; Popay, Ian; Champion, Paul; James, Trevor; Rahman, Anis (2004), An Illustrated Guide to Common Weeds of New Zealand (2nd ed.), New Zealand Plant Protection Society, ISBN 0473097605, OCLC 57620998, http://www.rnzih.org.nz/pages/chrysanthemoidesmonilifera.htm (Archived by WebCite)
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ CRC for Australian Weed Management (2003), Weed Management Guide – Boneseed - Chrysanthemoidesmonilifera ssp. monilifera., p. 1-2, http://www.weedscrc.org.au/documents/wmg_boneseed.pdf, retrieved on 2008-08-04 (Archived by the Wayback Machine)
^ Auld, BA; Medd, RW (1992), Weeds: an illustrated botanical guide to the weeds of Australia (Revised ed.), Melbourne, Vic., Australia: Inkata Press, p. 93, ISBN 0909605378, OCLC 16581672
^ ^a ^b Burgman, MA; Lindenmayer, DB (1998), Conservation Biology for the Australian Environment, Chipping Norton, NSW, Australia: Surrey Beatty & Sons, p. 141, ISBN 0949324787, OCLC 44708810
^ ^a ^b ^c ^d ^e ^f Parsons, WT (1973), Noxious weeds of Victoria, Melbourne, Vic., Australia: Inkata Press, p. 100-101, ISBN 0909605009, OCLC 874633
^ ^a ^b ^c Australian Institute of Agricultural Science (1976), The threat of weeds to bushland: A Victorian study, Melbourne, Vic., Australia: Inkata Press, p. 21-23
^ Thorp, JR; Lynch, R (2000), The Determination of Weeds of National Significance, Launceston, Tasmania, Australia: National Weeds Strategy Executive Committee, http://www.weeds.org.au/docs/WONS/, retrieved on 2008-08-04 (Archived by WebCite)
^ ^a ^b ^c Emert, S (2001), Gardener’s companion to weeds (2nd ed.), Sydney, NSW, Australia: Reed New Holland, p. 100, ISBN 1876334770, OCLC 52245716

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