Senecio hispidulus

Senecio hispidulus is an erect herb with an annual or a short lived perennial life cycle and can grow up to 2 metres (6 ft 7 in) tall, but is usually between 30–100 cm (12–39 in) tall.^[3] It is a dicotyledonous herb which means the plant is vascular and that it flowers. The plant flowers many small inflorescence of a yellow or pale-yellow color. The herb is sparsely to moderately course-hairy, with shorter hairs on upper leaf surface and longer, denser and jointed hairs on lower surface (A. Rich, 1834)^{[citation needed]}. The primary stem is usually simple and is covered in conspicuous soft bristly hairs. S. hispidulus has a woody base which develops into a ribbed mid stem. Mid stem leaves are evenly spaced and sized, usually 70–150 mm (2.8–5.9 in) in length. Its leaf color varying from dark green to yellow green and sometimes shaded with red. Also upper stem can be tinged with purple or red, and is usually triggered by environmental temperatures. The larger and lower leaf margins are sinuately pinnately lobed being usually three to five toothed, having a terminal tooth which is longer than that of the laterals. The uppermost smaller leaves, more in proximity to plant inflorescence are often dentate and not lobed. Plant inflorescence usually of many capitula (flower heads).^[4] Overall number of capitula contained usually between 14 and 48 containing 25 florets per capitula.^[5] Although this can be dependent on which component of S. hispidulus is found in New Zealand. Mature floret size usually between 6 mm and 12 mm long and 4 mm wide. The more mature and lobed leaves carry a very distinctive look to them, being a relatively narrow leaf. It has between 2 and 5 lobes along the side margins of the leaf. The seeds of S. hispidulus are hairy, which can be related to its name in Latin where senecio means 'old man' which can be linked to the 'bearded' or hairy seeds. S. hispidulus has small seeds usually around 0.5 mm wide and 2 mm long. In New Zealand S. hispidulus is represented by two components.^[5] These two components are geographically segregated as one grows in the area north of 39° south, where the other component grows to the south from that point. The main differences between the two components include the number of capitula and the number of florets per capitula counted on a mature plant. The northern component having 14 capitula counted, which contain between 26 and 31 florets each. Whereas the southern component counts 48 capitula with between 17 and 24 florets on each capitula.^[5]

S. hispidulus is indigenous to New Zealand and Australia. In Australia it is predominantly found in the state of New South Wales. Although S. hispidulus is also found in Tasmania, Western Australia, and Queensland.

In the North Island the dominant ranges of S. hispidulus are vicinity of Auckland isthmus, Coromandel, Ōpōtiki, and Wellington Province (A. Rich, 1934)^{[citation needed]}. In the South Island plant range includes Nelson, Marlborough, and North Canterbury. Although there is some variation in two recognized components among New Zealand material of S. hispidulus which has been collected. Whereby D. G. Drury suggests that the plants in the north of the North Island may have been naturalized in New Zealand, whereas there is little evidence to decide whether the plants from the northern South Island and Wellington area are indigenous or naturalized.^[4] As stated before the two components of S. hispidulus are geographically dispersed as there is a documented break in the range of S. hispidulus between latitude 38° and 40° south which separates the two components of S. hispidulus. This fact therefore does not support the hybridization hypothesis, which according to Drury "lacks support" on geographical basis.^[5]

The habitat of S. hispidulus can vary from coastal to montane environments, especially in sites where indigenous vegetation are burned or cleared recently.^[6] Usually growing in altitudes from sea level to 457 metres (1,500 ft) above sea level.^[5] The herb is prevalent in dry bare or disturbed habitats, such as recently cleared or burned areas. Primarily found in unstable environment. Also forest margins, coastal sites, and riverbeds are common place for S. hispidulus.^[7]

S. hispidulus can grow all year round depending on environmental circumstances, which is one of the reasons various specimens can have different heights. Some plants in good growing conditions can grow all year round, whereas other plants in suboptimal conditions will not be able to do this. This fact is one example of the versatility of the herb, which is able to easily adapt to its environment. This versatility is also demonstrated in the flowering period of S. hispidulus which is estimated to be from October to April, but is differently assessed by New Zealand Plant Conservation Network to last from August to May which is a very large time period for flowering to occur.^[8][3] But it is safe to say the plant flowers usually between spring and summer. S. hispidulus is known to be a strongly invasive species which is easily grown from seed. When flowering S. hispidulus produces both polliniferous (pollen bearing) florets and female florets. This is likely to increase the plants' probability to reproduce in a scenario where cross pollination might be hindered. A distinction in the number of polliniferous florets to female florets has been discovered between the two different components of S. hispidulus in New Zealand.^[5] The Northern component of S. hispidulus has been documented to grow between nine and eleven polliniferous florets per capitulum (cluster of small florets), whereas the southern component is recorded to carry between five and eight polliniferous florets per capitulum. Both the northern and southern components carry a more equal number of female florets compared to the florets with the polliniferous stamen. This might indicate a different need for pollen carrying flowers between the two S. hispidulus components in New Zealand.