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''Xylomelum'' is a
genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of six species of flowering plants, often commonly known as woody pears, in the family
Proteaceae The Proteaceae form a family (biology), family of flowering plants predominantly distributed in the Southern Hemisphere. The family comprises 83 genus, genera with about 1,660 known species. Australia and South Africa have the greatest concentr ...
and are
endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...
to Australia. Plants in this genus are tall shrubs or small trees with leaves arranged in opposite pairs, relatively small flowers arranged in spike-like groups, and the fruit a woody, more or less pear-shaped follicle.


Description

Plants in the genus ''Xylomelum'' are shrubs or trees that typically grow to a height of and have simple, leathery leaves arranged in opposite pairs. Juvenile leaves have coarse, sometimes prickly teeth on the edges. The flowers are arranged in dense, spike-like
raceme A raceme () or racemoid is an unbranched, indeterminate growth, indeterminate type of inflorescence bearing flowers having short floral stalks along the shoots that bear the flowers. The oldest flowers grow close to the base and new flowers are ...
s or
panicle In botany, a panicle is a much-branched inflorescence. (softcover ). Some authors distinguish it from a compound spike inflorescence, by requiring that the flowers (and fruit) be pedicellate (having a single stem per flower). The branches of a p ...
s, the flowers in pairs with a
bract In botany, a bract is a modified or specialized leaf, associated with a reproductive structure such as a flower, inflorescence axis or cone scale. Bracts are usually different from foliage leaves in size, color, shape or texture. They also lo ...
at the base. Each flower has four similar
tepal A tepal is one of the outer parts of a flower (collectively the perianth). The term is used when these parts cannot easily be classified as either sepals or petals. This may be because the parts of the perianth are undifferentiated (i.e. of very ...
s that roll back as the flower develops revealing four
stamen The stamen (: stamina or stamens) is a part consisting of the male reproductive organs of a flower. Collectively, the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filament ...
s. The fruit is a woody, more or less pear-shaped follicle attached at the larger end, that eventually splits into two halves and releases two winged seeds.


Taxonomy

The genus ''Xylomelum'' was first formally described in 1798 by James Edward Smith in ''
Transactions of the Linnean Society of London The Linnean Society of London is a learned society dedicated to the study and dissemination of information concerning natural history, evolution, and taxonomy. It possesses several important biological specimen, manuscript and literature collec ...
''. The name ''Xylomelum'' is derived from the Greek ''xylon'' meaning "wood" and ''melon'' "tree-fruit", referring to the woody fruit. In 1979, Farr, Leussink and Stafleu nominated ''Xylomelum pyriforme'' (Gaertn.) R.Br. as the
lectotype In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to anchor or centralizes ...
, later corrected to ''Xylomelum pyriforme'' (Gaert.) Knight.


Evolution

The "pears" of ''Xylomelum'' species are thought to have evolved primarily as a defense against
seed predation Seed predation, often referred to as granivory, is a type of plant-animal interaction in which granivores (seed predators) feed on the seeds of plants as a main or exclusive food source,Hulme, P.E. and Benkman, C.W. (2002) "Granivory", pp. 13 ...
. However, these woody fruits also provide protection of the seeds from fire. Johnson and Briggs (1963) consider the woody seeds in
Proteaceae The Proteaceae form a family (biology), family of flowering plants predominantly distributed in the Southern Hemisphere. The family comprises 83 genus, genera with about 1,660 known species. Australia and South Africa have the greatest concentr ...
to be a late evolutionary adaptation to fire.Johnson, L.A.S. & Briggs, B.G. 1963. Evolution in the Proteaceae, ''Australian Journal of Botany'', 11:21-61


Species list

The following is a list of species accepted by the
Australian Plant Census The Australian Plant Census (APC) provides an online interface to currently accepted, published, scientific names of the vascular flora of Australia, as one of the output interfaces of the national government Integrated Biodiversity Information Sys ...
as at November 2020: * '' Xylomelum angustifolium'' Meisn. (W.A.) * '' Xylomelum benthamii''
Orchard An orchard is an intentional plantation of trees or shrubs that is maintained for food production. Orchards comprise fruit tree, fruit- or nut (fruit), nut-producing trees that are generally grown for commercial production. Orchards are also so ...
(Qld.) * '' Xylomelum cunninghamianum'' Foreman (Qld., N.S.W.) * '' Xylomelum occidentale'' R.Br. (W.A.) * '' Xylomelum pyriforme'' ( Gaertn.)
Knight A knight is a person granted an honorary title of a knighthood by a head of state (including the pope) or representative for service to the monarch, the church, or the country, especially in a military capacity. The concept of a knighthood ...
(N.S.W.) * '' Xylomelum scottianum'' ( F.Muell.) F.Muell. (Qld.) A seventh species, ''Xylomelum salicinum''
A.Cunn. Allan Cunningham (13 July 1791 – 27 June 1839) was an English botanist and explorer, primarily known for his expeditions into uncolonised areas of eastern Australia to collect plants and report on the suitability of the land for grazing ...
ex R.Br.
is listed at
Plants of the World Online Plants of the World Online (POWO) is an online taxonomic database published by the Royal Botanic Gardens, Kew. History Following the Convention on Biological Diversity, the Royal Botanic Gardens in Kew launched Plants of the World Online i ...
but is regarded as a
synonym A synonym is a word, morpheme, or phrase that means precisely or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are a ...
of '' X. scottianum'' by the Australian Plant Census. In 2007, Anthony Edward Orchard suggested that ''X. salicinum'' (Meisn.) Benth. is a superfluous, illegitimate name and raised ''X. pyriforme'' var. ''salicinum'' Meisn. to species status as '' X. benthamii''. In 1788,
Joseph Gaertner Joseph Gaertner (12 March 1732 – 14 July 1791) was a German botanist, best known for his work on seeds, ''De Fructibus et Seminibus Plantarum'' (1788-1792). Biography He was born in Calw, and studied in Göttingen under Albrecht von Haller. H ...
described ''Banksia pyriformis'' in '' De Fructibus et Seminibus Plantarum'', a species whose genus was effectively reclassified when Smith described the genus, ''Xylomelum'' in 1798. Smith gave the essential characters of ''Xylomelum'' as: flower spikes with simple scales; flowers with four petals bearing four stamens, with a blunt, club-shaped stigma, with a uni-locular capsule having two seeds, the seeds being winged. In 1810,
Robert Brown Robert Brown may refer to: Robert Brown (born 1965), British Director, Animator and author Entertainers and artists * Washboard Sam or Robert Brown (1910–1966), American musician and singer * Robert W. Brown (1917–2009), American printmaker ...
gave a key to the genera of
Proteaceae The Proteaceae form a family (biology), family of flowering plants predominantly distributed in the Southern Hemisphere. The family comprises 83 genus, genera with about 1,660 known species. Australia and South Africa have the greatest concentr ...
in ''
Transactions of the Linnean Society of London The Linnean Society of London is a learned society dedicated to the study and dissemination of information concerning natural history, evolution, and taxonomy. It possesses several important biological specimen, manuscript and literature collec ...
'', placing ''Xylomelum'' in the group of
Proteaceae The Proteaceae form a family (biology), family of flowering plants predominantly distributed in the Southern Hemisphere. The family comprises 83 genus, genera with about 1,660 known species. Australia and South Africa have the greatest concentr ...
which have
dehiscent Dehiscence is the splitting of a mature plant structure along a built-in line of weakness to release its contents. This is common among fruits, anthers and sporangia. Sometimes this involves the complete detachment of a part. Structures that op ...
fruit and are unilocular with two seeds, thereby grouping '' Anadenia'', '' Grevillea'', ''
Hakea ''Hakea'' ( ) is a genus of about 150 species of flowering plants in the family ''Proteaceae'', endemic to Australia. They are shrubs or small trees with leaves that are sometimes flat, otherwise circular in cross section in which case they are s ...
'', '' Lambertia'', '' Orites'' and '' Rhopala'' together. Within the group, ''Xylomelum'' is distinguished from '' Orites'' and '' Rhopala'' by having winged seeds, a thickened woody follicle with an excentric
locule A locule (: locules) or loculus (; : loculi) is a small cavity or compartment within an organ or part of an organism (animal, plant, or fungus). In angiosperms (flowering plants), the term ''locule'' usually refers to a chamber within an ovary ...
, and a club-shaped stigma. In 1888, Engler, in '' Die Natürlichen Pflanzenfamilien'', divided the
Proteaceae The Proteaceae form a family (biology), family of flowering plants predominantly distributed in the Southern Hemisphere. The family comprises 83 genus, genera with about 1,660 known species. Australia and South Africa have the greatest concentr ...
into two sub-families, Persoonioideae and Grevilloideae, placing ''Xylomelum'' in Grevilloideae, and as being like '' Helicia'' in having the flower axis at the base with four glands, but differing from it by having the inflorescence in 'ears', not in loose 'grapes', and by having seeds with wings. In 1975,
Johnson Johnson may refer to: People and fictional characters *Johnson (surname), a common surname in English * Johnson (given name), a list of people * List of people with surname Johnson, including fictional characters *Johnson (composer) (1953–2011) ...
and Briggs placed ''Xylomelum'' in the subfamily
Grevilleoideae The Grevilleoideae are a subfamily of the plant family Proteaceae. Mainly restricted to the Southern Hemisphere, it contains around 46 genus, genera and about 950 species. Genera include ''Banksia'', ''Grevillea'', and ''Macadamia''. Descriptio ...
and the tribe Heliciaea (together with '' Helicia'', '' Triunia'' and '' Hollandaea'').Johnson, L.A.S. & Briggs, B.G. 1975. On the Proteaceae-the evolution and classification, ''Botanical Journal of the Linnean Society'' 70(2): 83-182 However,
Weston Weston may refer to: Places Australia * Weston, Australian Capital Territory, a suburb of Canberra * Weston, New South Wales * Weston Creek, a residential district of Canberra * Weston Park, Canberra, a park Canada * Weston, Nova Scotia * W ...
and Barker (2006), argue that within the tribe of Roupaleae, ''Xylomelum'' should be placed in the subtribe of Lambertiinae and not together with the '' Helicia'' in the subtribe of Heliciinae, using in part, the evidence of the molecular studies of Hoot and Douglas,Hoot, S.B. and Douglas, A.W. 1998. Phylogeny of Proteaceae based on atpB and atpB-rbcL intergenic spacer region sequences. ''
Australian Systematic Botany ''Australian Systematic Botany'' is an international peer-reviewed scientific journal published by CSIRO Publishing. It is devoted to publishing original research, and sometimes review articles, on topics related to systematic botany, such as b ...
'' 11: 301-320
who pair ''Xylomelum'' with '' Lambertia''. See
Grevilleoideae The Grevilleoideae are a subfamily of the plant family Proteaceae. Mainly restricted to the Southern Hemisphere, it contains around 46 genus, genera and about 950 species. Genera include ''Banksia'', ''Grevillea'', and ''Macadamia''. Descriptio ...
for further discussion of the placement of ''Xylomelum'' within the
Proteaceae The Proteaceae form a family (biology), family of flowering plants predominantly distributed in the Southern Hemisphere. The family comprises 83 genus, genera with about 1,660 known species. Australia and South Africa have the greatest concentr ...
.


Distribution and habitat

Two species, '' X. angustifolium'' and '' X. occidentale'', are endemic to Western Australia and the remaining five species are found in New South Wales and Queensland. All are either mesophytes or grow in dry environments.


References

{{Taxonbar, from=Q2707698 Proteaceae genera Proteales of Australia Trees of Australia Taxa named by James Edward Smith Endemic flora of Australia