Lysiana Exocarpi

''Lysiana exocarpi'', commonly known as harlequin mistletoe, is a species of hemiparasitic shrub, endemic to Australia. It is in the Gondwanan family Loranthaceae and is probably the most derived genus of that family with 12 pairs of chromosomes. The Loranthaceae is the most diverse family in the mistletoe group with over 900 species worldwide and including the best known species in Australia. Mistletoes are notable for their relationships with other species. In an early reference to the group in Australia Allan Cunningham explorer and first Director of the Royal Botanic Gardens, Sydney, wrote in 1817: "The Bastard Box is frequently much encumbered with the twining adhering ''Loranthus aurantiacus'' (box mistletoe) which 'Scorning the soil, aloft she springs, Shakes her red plumes and claps her golden wings'."

Description

Spreading to shrub, glabrous; no external runners.
Leaves flat or compressed when very narrow, linear to narrow-oblong, sessile or the wider leaves shortly petiolate, 3–15 cm long, 1–10 mm wide, apex is usually rounded, base attenuate - contracted, venation is obscure; shortly petiolate.
Inflorescence pedunculate usually a 2-flowered umbel; peduncle usually 0.5–2 mm in length; pedicels 2–5 mm long; bracts 1–1.5 mm long. Corolla 25–50 mm long, is usually red, rarely yellow, can also be tipped with green or black.
Fruit ellipsoidal to ovoid, 6–10 mm long, red or black.

Subspecies

''Lysiana exocarpi'' subsp. ''exocarpi''

Leaves are linear to narrow-oblong or narrow-elliptic and occasionally obcordate, 3–10 mm wide, often thick or leathery at maturity. Plant spreading to pendent. Mostly parasitic on species of ''Acacia'', ''Alectryon'', ''Amyema'', ''Cassia'', Casuarinaceae, ''Eremophila'', ''Exocarpos'', and exotic trees, west from Moree district. Synonym: ''L. exocarpi'' subsp. ''diamantinensis''

''Lysiana exocarpi'' subsp. ''tenuis''

Leaves linear, 1–3 mm wide, not terete but sometimes compresses. Plant is pendent. It is found in open woodland and forest, usually on species of Casuarinaceae, north from the Hunter Valley First described in 1925 by Blakely as ''Loranthus exocarpi'' var. ''tenuis'' and revised by Barlow in 1963 to ''Lysiana exocarp''i subsp.t''enuis''.

Habitat and distribution

''Lysiana'' species can be broadly grouped into those that have 80-90 units of DNA and those that have greater than 100 units. ''L. exocarpi'' is the only species that extends its range into temperate non-arid regions, with DNA values predominantly above 100, the average being 117 units.

Open woodland and forest, extending into semi-arid woodlands dominated by acacia.

''L. exocarpi:'' Occurs in arid and temperate regions of all mainland States, from Lake Carnegie, W.A, to the Hunter Valley, NSW, in open forest and woodland on many different hosts but frequently on other Loranthaceae.

''L. exocarpi'' subsp. ''exocarpi'': Occurs in arid and temperate Australia from Lake Carnegie, Q.A., to western Qld and central Vic; on many host species, most frequently on ''Acacia'', ''Amyema'', '' Cassia'', Casuarinaceae, '' Eremophila'', ''Exocarpos'', '' Alectryon'' and exotic trees. A polymorphic subspecies, with a cline towards wider and thicker leaves from temperate to arid habitats.

''L. exocarpi'' subsp. ''tenuis:'' Occurs in Qld and NSW from the Darling Downs to the Hunter Valley and inland to the Western Plains, in open woodland and forest, usually on Casuarinaceae.

Life cycle

Flowering and germination

Flowering occurs mainly in summer. Charles Brittlebank (1908) noted that germination "usually takes place in one to two days, but may be delayed in some cases for a period of 50 days".

Fire responses

Life span - 4 to 20 years. First seeds - 2 to 3 years. Adult fire response - greater than a 70% mortality when subject to total leaf scorch. Resprouting - none.

Parasitism

Mistletoes generally have green or green-yellow coloured leaves and stems and photosynthesise. However, they use the water supply of the host plant and the water-soluble nutrients in the water (sap). For this reason, they are considered to be semi-parasites. Attachment to the host plant is by means of one or more woody absorbing organs (haustoria). This organ effectively replaces the root system of a normal plant, and extends through the bark layers of the host and into the young wood zone, where most of the water transport occurs.

Mistletoes often have foliage that mimics the host plant.

''Lysiana exocarpi'' is known to ''epiparasitise'' other mistletoes, namely ''Amyema'' species: ''A. maidenii'', ''A. miquelii'' (box mistletoe), ''A. quandang''

Host plants

In New South Wales the most common hosts are species of ''Eucalyptus'' and ''Acacia'' and also ''Flindersia'', ''Pittosporum'', ''Santalum''
In a comprehensive study of Australian herbaria specimens, Paul Downey found that the host plants for Australian mistletoes were mostly dicotyledonous angiosperms with a small number of gymnosperms in the genera ''Araucaria'', ''Callitris'' and ''Pinus''. No host species were herbaceous. Every host family and genus recorded contained species which were not documented as mistletoe host species. The two major genera of host species were ''Eucalyptus'' and ''Acacia'' with 2084, and 2559 records respectively. There were 187 species of ''Eucalyptus'' and 150 species of ''Acacia''. Seven mistletoe species commonly parasitised exotic host species including ''L. exocarpi''. The commonly recorded exotic host species included ''Nerium oleander'', ''Citrus'' spp., ''Prunus'' spp., ''Schinus molle'' and ''Quercus'' spp.
''L. exocarpi'' was found in 901 records and 109 species. The host families were Apocynaceae, Caesalpiniaceae, Capparaceae, Casuarinaceae, Chenopodiaceae, Fabaceae, Fagaceae, Loranthaceae, Malvaceae, Meliaceae, Mimosaceae, Moraceae, Myoporaceae, Myrtaceae, Oleaceae, Pittosporaceae, Polygonaceae, Proteaceae, Rhamnaceae, Rutaceae, Santalaceae, Sapindaceae, Solanaceae and Zygophyllaceae. In a 1990 study of ''L. exocarpi'' subsp. ''exocarpi'' in Southern South Australia, Yan found that this species showed a specific preference for ''Alectryon oleifolius'' and ''Myoporum platycarpum'' supporting Barlow's view that all Australian mistletoes of open forest and woodland are host specific to some extent. He also found that rainfall was a determining factor in regulating the distribution.

Insect and animal associations

Interactions between mistletoes and animals have long been noted and were used by Charles Darwin as early exemplars of evolutionary adaptation with Carl Linnaeus credited as the first to describe the mistletoe life cycle. Pliny the Elder had recorded similar observations some 1600 years earlier. Most species of mistletoe are dispersed by animals, chiefly birds and this close relationship has been treated as a model system in the study of fruit dispersal generally. Many insects pollinate mistletoes primarily in the Coleoptera, Diptera, Hymenoptera and Lepidoptera.

At least 27 species of Australian butterflies use mistletoes as their host plant. The two groups are the jezebels (Pieridae) and azures (Lycaenidae). Upon hatching, the caterpillars subsist and grow entirely on the foliage. Although some species drop off to pupate in the ground beneath, most remain in the clump attaching their chrysalis to the tips of denuded twigs or burrowing into the junction between mistletoe and the host tree to evade predators. ''L. exocarpi'' is a host plant for ''Ogyris aenone'' and is a popular food plant for nectar feeding birds when in full flower.

The mistletoe fruit is a single-seeded berry, often brightly coloured, with striking adaptations for bird dispersal, germination and attachment. Under the outer coat of the fruit is a sticky layer of viscin