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17-548: Testulea is a monotypic genus of plants in the family Ochnaceae . It contains only one species, Testulea gabonensis , an endangered species native to Central Africa . T. gabonensis is native to Cameroon , Equatorial Guinea , Gabon , and the Republic of the Congo , where it grows in primary rainforests . It is usually scattered at low densities throughout its habitat and prefers humid, well-drained locations. T. gabonensis

34-602: A common ancestor ) or paraphyletic (excluding some descendants), these concepts do not apply to monotypic taxa because they contain only a single member. Monotypic taxa are part of a broader challenge in biological classification known as aphyly – situations where evolutionary relationships are poorly supported by evidence. This includes both monotypic groups and cases where traditional groupings are found to be artificial. Understanding how monotypic taxa fit into this bigger picture helps identify areas needing further research. The German lichenologist Robert Lücking suggests that

51-482: A hierarchical system. When taxonomists identify a monotypic taxon, this often reflects uncertainty about its relationships rather than true evolutionary isolation . This uncertainty is evident in many cases across different species. For instance, the diatom Licmophora juergensii is placed in a monotypic genus because scientists have not yet found clear evidence of its relationships to other species. Some taxonomists argue against monotypic taxa because they reduce

68-407: A monophyletic group, the clade AB. Clade AB and taxon C are also sister groups. Taxa A, B, and C, together with all other descendants of their MRCA form the clade ABC. The whole clade ABC is itself a subtree of a larger tree which offers yet more sister group relationships, both among the leaves and among larger, more deeply rooted clades. The tree structure shown connects through its root to

85-655: A family. Some examples of monotypic groups are: Sister group In phylogenetics , a sister group or sister taxon , also called an adelphotaxon , comprises the closest relative(s) of another given unit in an evolutionary tree . The expression is most easily illustrated by a cladogram :   Taxon A       Taxon B       Taxon C               More tree branches   Taxon A and taxon B are sister groups to each other. Taxa A and B, together with any other extant or extinct descendants of their most recent common ancestor (MRCA), form

102-553: A natural classification. From a cladistic perspective, which focuses on shared derived characteristics to determine evolutionary relationships, the theoretical status of monotypic taxa is complex. Some argue they can only be justified when relationships cannot be resolved through synapomorphies (shared derived characteristics); otherwise, they would necessarily exclude related species and thus be paraphyletic. However, others contend that while most taxonomic groups can be classified as either monophyletic (containing all descendants of

119-414: Is birds , whose commonly cited living sister group is the crocodiles , but that is true only when discussing extant organisms ; when other, extinct groups are considered, the relationship between birds and crocodiles appears distant. Although the bird family tree is rooted in the dinosaurs , there were a number of other, earlier groups, such as the pterosaurs , that branched off of the line leading to

136-455: Is a medium to large tree growing up to 50 m (160 ft) tall. The trunk is typically straight and cyclindrical, growing up to 120 cm (47 in) in diameter, with steep butresses up to 3 m (9.8 ft) high. The yellowish-grey or yellowish-brown bark is scaly and falls away in small patches. The leaves are oblanceolate in shape, measuring 20–35 cm (7.9–13.8 in) long and 4–8 cm (1.6–3.1 in) wide. The tip of

153-402: Is known as "Gregg's Paradox": if a single species is the only member of multiple hierarchical levels (for example, being the only species in its genus, which is the only genus in its family), then each level needs a distinct definition to maintain logical structure. Otherwise, the different taxonomic ranks become effectively identical, which creates problems for organizing biological diversity in

170-482: Is listed as endangered by the International Union for Conservation of Nature under criterion A1cd, based on its declining population and continued exploitation for timber. It is overexploited in much of its range, and is vulnerable due to its small distribution and low density. Monotypic taxon Monotypic taxa present several important theoretical challenges in biological classification . One key issue

187-407: Is particularly associated with island species. Among 25 documented extinct monotypic genera studied, 22 occurred on islands, with flightless animals being particularly vulnerable to human impacts. Just as the term monotypic is used to describe a taxon including only one subdivision, the contained taxon can also be referred to as monotypic within the higher-level taxon, e.g. a genus monotypic within

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204-745: The common application of the term monotypic is frequently misleading, "since each taxon by definition contains exactly one type and is hence "monotypic", regardless of the total number of units", and suggests using "monospecific" for a genus with a single species, and "monotaxonomic" for a taxon containing only one unit. Species in monotypic genera tend to be more threatened with extinction than average species. Studies have found this pattern particularly pronounced in amphibians , where about 6.56% of monotypic genera are critically endangered , compared to birds and mammals where around 4.54% and 4.02% of monotypic genera face critical endangerment respectively. Studies have found that extinction of monotypic genera

221-427: The information content of biological classifications. As taxonomists Backlund and Bremer explain in their critique, "'Monotypic' taxa do not provide any information about the relationships of the immediately subordinate taxon". When monotypic taxa are sister to a single larger group, they might be merged into that group; however, when they are sister to multiple other groups, they may need to remain separate to maintain

238-525: The leaf is short and pointed, and the edges are slight wavy. The leaves are arranged spirally, clustering near the tips of the branches. The inflorescence is a false raceme that grows up to 35 cm (14 in) long, with flowers arranged in groups of three or four. The bisexual flowers are zygomorphic and tetramerous . The flowers may be yellowish-white to pink in colour and are borne on pedicels measuring approximately 1.5 cm (0.59 in) long. The petals and sepals are of unequal sizes, with

255-472: The petals ranging from 1 cm (0.39 in) to 1.5 cm (0.59 in) long. Several staminodes are fused to form a long tube. The fruit is a rounded, flattened capsule measuring 3–6 cm (1.2–2.4 in) in diameter with a notch at the top. The seeds are cyclindrical, measuring around 1 cm (0.39 in) long, with a papery wing that measures around 1.5 cm (0.59 in) long. T. gabonensis typically flowers from December to April, with

272-430: The rest of the universal tree of life . In cladistic standards, taxa A, B, and C may represent specimens, species , genera , or any other taxonomic units. If A and B are at the same taxonomic level, terminology such as sister species or sister genera can be used. The term sister group is used in phylogenetic analysis , however, only groups identified in the analysis are labeled as "sister groups". An example

289-420: The seeds dispersed by wind. Grey parrots are known to feed on the seeds. The wood of T. gabonensis is durable and may be used as a substitute for teak . It is traded on the international timber market under the name izombé , and is used is used for boat-building , construction, furniture, mine props , sporting equipment, sculpting, and turnery . The bark is used in traditional medicine . T. gabonensis

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