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Hyptis (Hyptis suaveolens) is an erect annual or short-lived perennial herb commonly growing to about 1.5 m tall, rarely to 3 m and strongly aromatic when crushed. Its stems are green or reddish-green, extremely hairy and square in cross-section. Leaves are oppositely arranged and hairy; the leaf blade is usually ovate (egg-shaped), elliptic (oval) or slightly cordate (heart-shaped) in outline, about 2 to 10 cm long and 1 to 7 cm wide and quite hairy with shallow teeth along the margins.
The pinkish or lavender-blue flowers are about 5 to 7 mm long and are arranged singly or in clusters of up to 5 in the axils of the upper leaves. After the flowers die the corolla is lost, but the tubular calyx persists and turns brown and is very distinctive, with each of the five lobes topped by a bristle about 5 mm long. The fruit held within the calyx is a lobed capsule that divides into two 'nutlets', each of which contains a single seed. The 'nutlets' are dark brown to black in colour with whitish markings at one end and are flattened and shield-shaped and 3 to 4 mm long and 2.5 to 3 mm wide (Parsons & Cuthbertson 2001; Miller & Schultz 2002; Navie 2004).
Also see Smith (2002) and Wilson et al. (2004) for illustrations.
For further information and assistance with identification of Hyptis contact the herbarium in your state or territory.
Hyptis favours fertile, coarse-textured, non-waterlogged soils in mostly tropical and subtropical regions. It is common as a roadside weed and in overgrazed native and 'improved' pastures. It is often noted around stockyards and watering holes (Parsons & Cuthbertson 2001; Miller & Schultz 2002).
Hyptis is a distinctive species and is usually readily identified. It may be confused with Hyptis capitata but, among other things, that species has white flowers which are borne in globular clusters and the leaves are hairless or only sparsely hairy, not conspicuously hairy (Navie 2004).
Hyptis was included in the list of 71 species that were nominated by state and territory governments for assessment as Weeds of National Significance (WONS). Following an assessment process, Hyptis was not included as one of the 20 WONS. However, it remains a weed of potential national signficance.
Hyptis is unpalatable to stock and in overgrazed areas will form dense thickets which render infested areas unproductive. It can be a serious competitor in grain crops and peanut crops (Parsons & Cuthbertson 2001; Miller & Schultz 2002).
Hyptis also invades woodlands, open forests and watercourses and forms dense thickets on flood plain margins (e.g. Smith 2002, Navie 2004).
Hyptis is spread by seed, which normally remains in the bristly fruit, readily attaching to animals and clothing. It is also spread by water, machinery and vehicles and is a common contaminant of hay (Parsons & Cuthbertson 2001).
The earliest record of Hyptis in Australia is of a collection made by Ludwig Leichhardt, with it being recorded by George Bentham in 1870, as collected from Garden Bay, Port Essington, on the Coburg Peninsula in the Northern Territory. It would have been collected in either December 1845 or January 1846. The fact that it was in a garden indicates that Hyptis is definitely not native, but a deliberate or accidental addition to the garden. The species was also deliberately introduced to Darwin from Timor by a Mr Schmidt (Holtze 1892). This was seemingly in the early 1870s or perhaps slightly earlier and for some time the plant was known as Schmidt's Folly.
Small infestations of Hyptis can be removed manually before seeding. In pasture areas, light to moderate grazing in association with the use of perennial climbing legumes such as Calopo (Calopogonium mucunoides) gives effective control, whereas mowing or slashing provides only temporary relief. However, chemical control usually gives better results, with spraying best applied before flowering begins. An early application in November, followed by a second spraying in February to kill late-germinated seedlings, is often desirable.
Exploration for suitable biological control commenced in 1980 but, with the possible exception of a rust, no specific agents had been found (Parsons & Cuthbertson 2001).
Please see the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au .
In northern Australia Hyptis seed germinates mostly in October and November after the opening rains at the end of the dry season, with intermittent germination occurring during the wet season. Flowering occurs from about February to May. Most plants die during the dry season although those in well-watered areas may persist until the following year as short-lived perennials. The seeds are light-sensitive and will not germinate in shade (Parsons & Cuthbertson 2001).
NT, QLD, WA
Hyptis is found throughout much of northern Western Australia, northern Northern Territory (as far south as Barrow Creek) and much of northern Queensland. It is also found in south-east Queensland, such as in the Wide Bay region (Stanley & Ross 1986; Miller & Schultz 2002; Navie 2004).
Hyptis is native to the tropical regions of Central and South America. Now it is a widely dispersed weed found from east Africa to Papua New Guinea and the Pacific islands (Parsons & Cuthbertson 2001).
Horehound, Wide Spikenard, Pignut, Chinese Mint, Mint Weed, Chan