Mikania Micrantha Carol A

Profile of an Invasive Plant: 2 Mikania micrantha Carol A. Ellison1* and K.V. Sankaran2 1CABI, Egham, UK; 2Kerala Forest Research Institute (KFRI), Peechi, India Introduction predictors is appropriate with newly invasive species. However, there are some gen- Despite the long history of biological inva- eral factors that are either likely to operate sions in the Asia–Pacific region, little has or known to be important in facilitating an been achieved in terms of effective manage- exotic species to become invasive: for exam- ment actions for such species. This situation ple, similarities in climate and soil between needs be remedied given that: (i) many crop the original habitat of the exotic species and species are affected, thereby threatening the its new habitat (Nye and Greenland, 1960; food security of all countries in the region; Holgate, 1986); and the absence of all or (ii) the region has a great diversity of habi- most of its co-evolved, host-specific natural tats, rich biodiversity and a high level of spe- enemies (which were present in the original cies endemism; (iii) many endemic species habitat) from the adventive range (as men- and their habitats in the region are threat- tioned in the next paragraph). ened; and (iv) the degradation and fragmen- Some of the most damaging invasive tation of natural habitats are common. Thus, alien species are plants. Plant species have damage due to invasive alien species is argu- been moved around the world by humans ably higher in this region than in other parts for centuries – either deliberately as crops of the world. and ornamental species, or accidently as Although the threat posed by invasive casual passengers. Most of these species do species to livelihoods and biodiversity is not become invasive in their introduced now high profile, the mechanisms by which range. Moreover, plants are usually moved an invasive species succeeds are largely ill- without most or all of the natural enemies defined. A fundamental understanding of referred to above, and, often aided by human these mechanisms might eventually allow disruption of natural habitats, population the prediction of which species will become explosions of some species occur, with the invasive and, therefore, the development subsequent development of plant invasions of more effective management strategies (Mack et al., 2000). The Neotropical plant (Deng et al., 2004). Nevertheless, at present Mikania micrantha Kunth illustrates the lat- it remains difficult to predict whether a spe- ter situation very well, and it is used as a cies that establishes in a new environment core example by most of the authors in this will become invasive or not. The best predic- volume. In its native range, the species tors of invasiveness for plants are whether generally has a cryptic riparian non-weedy the species has such a history elsewhere and habit, and grows along riverbanks and whether it reproduces vegetatively (Kolar among reed-like vegetation around standing and Lodge, 2001), but neither of these water (Cock, 1982; Barreto and Evans, * Corresponding author. E-mail: [email protected] CAB International 2017. Invasive Alien Plants 18 (eds C.A. Ellison, K.V. Sankaran and S.T. Murphy) Profile of an Invasive Plant: Mikania micrantha 19 1995). None the less, since the plant was Taxonomy, Description and Distribution introduced into Asia at various times in the 20th century as a cover crop, and for various M. micrantha was described in 1818 by other purposes (see next section: Taxonomy, Kunth (Humboldt et al., 1818). Common description and distribution), the environ- English-language names for the species ments in Asia and the Pacific have allowed it include mikania weed, American rope, bit- to express a full, or near-full, capacity for tervine, climbing hemp vine and Chinese reproduction, growth and spread across creeper. Although it is also commonly called many types of ecosystems. As a result, mile-a-minute weed, this name is best M. micrantha has become a serious threat to avoided as it is also used for the for the unre- a range of crop plants and to native plants, lated weed Persicaria perfoliata in the USA. particularly in India in the high-biodiversity The classification of the species is as areas of the Western Ghats and in the state follows: of Meghalaya (Bhatt et al., 2012; and Chap- ter 1, this volume). Class: Dicotyledonae Here, current information on the tax- Subclass: Asteridae onomy and distribution of M. micrantha are Order: Asterales summarized, followed by a review of rele- Family: Asteraceae (Compositae) vant details on its life cycle and physiological Subfamily: Asteroideae ecology. The last of these topics has received Tribe: Eupatorieae much attention over recent years and Species: Mikania micrantha Kunth advances have been made in particular on Mikania is a species-rich genus with the allelopathic properties and photosyn- over 425 described species (King and Robin- thetic strategy of the plant. Additional son, 1987). Almost all are New World native information about its physiology has been species, with only nine being considered elucidated from a comparison with M. cor- native to the Old World, and only one of data, which is native to Asia (Deng et al., these, M. cordata (Burm. f.) Robinson, being 2004). These topics form an important back- native to Asia (Holmes, 1982). There has drop for the book, because the theme of how been considerable confusion over the cor- some of the plant’s biological traits have rect identification of M. micrantha in Asia, facilitated population outbreaks in agro- with early literature mistakenly referring to ecosystems and disturbed native ecosystems it as M. scandens (L.) Willd. (a North Ameri- owing to the nature of these habitat types is can species) or M. cordata. However, Parker pursued by authors in a number of chapters (1972) concluded that M. micrantha is the in this volume. The topic of the role of the only species that causes a significant weed natural enemies in suppressing plant inva- problem, and this was confirmed by the sions is discussed separately in Chapter 10, work of Holmes (1982). this volume. M. micrantha is a fast-growing, peren- Lastly, another consequence of the nial, creeping or twining vine. A full taxo- domination of M. micrantha in many habi- nomic description from Holm et al. (1991) is tats in the Asia–Pacific region is that several as follows: rural communities have been driven to seek ways of exploiting the plant, and these have stems branched, pubescent to glabrous, been largely based on its perceived traits and ribbed; leaves opposite, thin, cordate, properties. The reported benefits are few, triangular, or ovate, blade 4 to 13 cm long, but they are reviewed at the end of this 2 to 9 cm wide, on a petiole 2 to 8 cm long, base cordate or somewhat hastate, tip chapter in order to complete the species acuminate, margins coarsely dentate, profile. crenate, or subentire, both surfaces A general data sheet on M. micrantha glabrous, three- to seven-nerved from base; can be found in the open-access CABI Inva- flowers in heads 4.5 to 6 mm long, in sive Species Compendium (available at: terminal and lateral openly rounded, www.cabi.org/isc/datasheet/34095). corymbous panicles; involucral bracts four, 20 Carol A. Ellison and K.V. Sankaran oblong to obovate, 2 to 4 mm long, acute, that are 2–3 mm in length, while those of green, and with one additional smaller bract M. cordata are significantly longer (4–5 mm) 1 to 2 mm long; four flowers per head; and the seed is significantly larger. corollas white, 3 to 4 mm long; fruit in an M. micrantha is a plant of Neotropical achene, linear-oblong, 1.5 to 2 mm long, origin that has become invasive in most black, five-angled, glabrous; pappus of 32 to 38 mm long, soft white bristles 2 to 3 mm countries within the humid tropical zones of long. Asia and the Pacific (Waterhouse, 1994). It occurs from sea level up to 1500 m. The first The species possesses semi-translucent record of M. micrantha in Asia dates back to enations (small scaly leaf-like structures 1884, and is from the Hong Kong Zoological without vascular tissue) between the peti- and Botanical Gardens (Li et al., 2003). How- oles at the nodes of young vegetative shoots, ever, in Malaysia and Indonesia, evidence which are a rare feature in the Asteraceae. suggests that the plant was introduced on These are not seen on flowering branches a number of occasions, both to botanical and they wither on older shoots. Differences gardens and as a plantation cover crop in the form of the enations can help to dis- ( Wirjahardja, 1976; Holmes, 1982; Cock tinguish M. micrantha from M. cordata. The et al., 2000). It was recorded to have been enations of M. micrantha are membranous brought from Paraguay to Bogor Botanical flaps with incised lobes, whereasM. cordata Garden in West Java, where it was planted produces ear-like enations with furry ridges, for medicinal purposes in 1949 (Cock et al., which are not membranous (see Fig. 2.1a). 2000). Some scientists support the view The length of the pappus (the fine feathery that M. micrantha was introduced as a non- hairs that surround the fruit in the leguminous ground cover for crops in India Asteraceae) bristles on the seed is also a (Borthakur, 1977; Palit, 1981), and Parker distinguishing feature between the two (1972) reported that the plant was inten- species. Fig. 2.1b shows the structure of tionally introduced into north-eastern India M. micrantha seed, which has pappus bristles during the Second World War as ground a b Fig. 2.1.

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