Several conspicuous or unusual traits are characteristic of the family (whenTepuianthus is excluded). The bark is usually shiny and fibrous, with strips of bark peeling down the side of broken stems.[3] The number ofstamens is usually once or twice the number ofcalyx lobes; when twice, they often occur in two well separated series. Exceptions includeGonystylus, which may have up to 100 stamens, andPimelea, which has only 1 or 2.
Thymelaeaceae are often difficult to identify because of equivocal interpretation of the flower parts. Sepals, petals, andstaminodes are hard to distinguish, and many keys are ambiguous about whether staminodes should be counted as stamens. Moreover, inWikstroemia, individual plants often produce anomalous flowers.
The family is named from the genusThymelaea, the name of which is a combination of the Greek name for the herbthyme θύμος (thúmos) and that for theolive ἐλαία (elaía)—in reference to its thyme-like foliage (i.e. minuscule leaves) and olive-like fruit.[4]
The Thymelaeaceae are in the orderMalvales.[5] Except for a sister relationship withTepuianthaceae, little is known for sure about their relationships with the other families in theorder.[6]
Unlike most recent authors, who accept foursubfamilies, B. E. Herber has divided Thymelaeaceae into two subfamilies.[citation needed] He has retained the subfamily Gonostyloideae, but renamed it Octolepidoideae. The other three traditional subfamilies (Synandrodaphnoideae, Aquilarioideae, and Thymelaeoideae) were combined into a Thymelaeoideae s.l.(sensu lato), and reduced totribal rank, as Synandrodaphneae, Aquilarieae, and Daphneae, respectively. No tribes were designated in subfamily Octolepidoideae, but it was provisionally divided into two informal groups, the Octolepis group and the Gonystylus group. Likewise, nosubtribes were designated in the tribe Daphneae, but it was informally divided into four groups: theLinostoma group, theDaphne group, thePhaleria group, and theGnidia group. The 45 genera accepted by Herber are grouped as follows. Three genera in Daphneae were placedincertae sedis (not assigned to any particular group or in a separate group by themselves).
The first molecular phylogeny for Thymelaeaceae was published in 2002.[7] It was based on two regions ofchloroplastDNA. These were therbcLgene and theintergenic spacer between thetransfer RNA genestrnL andtrnF. Forty one species in the family were sampled. In 2008, Marline Rautenbach performed a phylogenetic study in which 143 species in the family were sampled. The sampling in this study was concentrated in theGnidia group, but the sampling in the rest of the family was as extensive as in the previous study, or more so. In addition to rbcL andtrnL-F data, sequences of the ITS (internal transcribed spacer) region ofnrDNA (nuclear ribosomal DNA) were used. All of the clades that were strongly supported in the previous study were recovered with even stronger statistical support.
The tree below is an excerpt from the Rautenbach (2002) phylogeny. The species ofGnidia were chosen from among the most common or well known species in a way that shows which clades contain species ofGnidia.
The striking flowers ofGnidia rubescensGnidia pinifolia in bloomGnidia glauca (known formerly asLasiosiphon glaucus)Detail of flowers ofGnidia glauca (known formerly asLasiosiphon glaucus)
Thecircumscription of genera in Thymelaeaceae has always been difficult, and is to some degree artificial. For example, the difficulty of distinguishingDaphne fromWikstroemia has been commented upon by Rautenbach and Herber.[8][9] Several small genera are probably embedded inDaphne orWikstroemia, or ifDaphne andWikstroemia are intermingled, these small genera might be embedded in both simultaneously.Stellera, for example, is nested withinWikstroemia, at least (see thephylogenetic tree below).
A recent comparison of DNA sequences has established themonophyly ofThymelaea and thepolyphyly ofDiarthron,[10] but there was not sufficient sampling inWikstroemia andDaphne to exclude the possibility thatThymelaea,Diarthron, and others might be embedded in them.
The large genusGnidia is polyphyletic and its species fall into four separate clades, each of which contains other genera of the family (see the phylogenetic tree below). Thetype species forGnidia isGnidia pinifolia. IfGnidia is divided into four or more separate genera, the segregate genus which containsG. pinifolia will retain the nameGnidia. Zachary S. Rogers published a revision of theGnidia of Madagascar in 2009 inAnnals of the Missouri Botanical Garden.
Some of the older treatments of Thymelaeaceae treatLasiosiphon as a separate genus fromGnidia. This distinction was later shown to be artificial. However, Van der Bank et al. (2002)[7] suggested thatLasiosiphon might be resurrected if redefined. The type species forLasiosiphon isGnidia glauca, formerly known asLasiosiphon glaucus.
Rautenbach used different names from Herber for some of the groups and placed some of the groups at different taxonomic rank, but her phylogeny supports Herber's classification with the few exceptions noted below. The only strongly supported difference (99%(bootstrap percentage) from Herber's classification was thatDais was found to be sister toPhaleria. The phylogeny casts significant doubt upon the monophyly of the subfamily Octolepidoideae, and upon the monophyly of the informalOctolepis andGonostylus groups, but this result had only weak statistical support. Only a sampling of more species and more DNA from each will determine whether these groups are monophyletic or not.Stephanodaphne andPeddiea might need to be transferred to theGnidia group, but support was not strong (60% BP) for a clade consisting of theGnidia group withStephanodaphne andPeddiea. Again, more extensive sampling will be required to resolve this question. Two of the three genera placed incertae sedis by Herber (Linodendron andLasiadenia) have not yet been sampled and their relationships to other genera remain obscure.
Herber (2003)[9] accepts 45 genera, excludingTepuianthus from the family, sinkingAtemnosiphon andEnglerodaphne intoGnidia,Eriosolena intoDaphne, andThecanthes intoPimelea.[9] The largest genera and the approximate number of species in each areGnidia (160),Pimelea (110),Daphne (95),Wikstroemia (70),Daphnopsis (65),Struthiola (35),Lachnaea (30),Thymelaea (30),Phaleria (30), andGonystylus (25).[9]
In the past, different authors have defined Thymelaeaceae in different ways. For example,John Hutchinson excludedGonystylus and its close relatives, as well asAquilaria and its close relatives from the family, forming two segregate families, Gonystylaceae and Aquilariaceae.[12] But today, the only controversy that still remains over the circumscription of the family is the question of whetherTepuianthus should be included, or segregated as a separate,monogeneric family.[13] Stevens includesTepuianthus, but Kubitzki treats Tepuianthaceae as a separate family.[14]
Lagetta lagetto the "lacebark": botanical illustration showing plant with samples of cordage and fabric made from its fibreIntricateJamaican souvenirs woven from "lacebark" fibreTheBrazilianFunifera utilis, its genus named from the suitability of its fibre for rope-making (under the obsolete nameLagetta funifera)
Several genera are of economic importance.Gonystylus (ramin) is valued for its comparatively soft, easily worked yellowish wood, but trade in all species in the genus is controlled byCITES. Many genera have inner bark yielding strongfibre suitable for the making ofcordage andpaper, a fact acknowledged in the naming of one of the genera,Funifera meaning the Latin for "bearer (provider) of rope". The bark ofAquilaria,Daphne,Edgeworthia,Gnidia,Linostoma,Rhamnoneuron,Thymelaea,Stellera, andWikstroemia are used in paper-making,[17] whileLagetta was once harvested as a source of naturallace for making doilies and trimmings for luxury garments.[18]
^The Royal Horticultural Society Dictionary of Gardening ed. Chittenden, Fred J., 2nd edition, by Synge, Patrick M. Volume III : Je-Pt. Pub. Oxford at the Clarendon Press 1965. Reprinted 1984.ISBN0-19-869106-8
^Clemens Bayer, Michael F. Fay, Anette Y. de Bruijn,Vincent Savolainen, Cynthia M. Morton, Klaus Kubitzki, William S. Alverson, and Mark W. Chase (1999). "Support for an expanded family concept of Malvaceae within a recircumscribed order Malvales: a combined analysis of plastid atpB and rbcL DNA sequences".Botanical Journal of the Linnean Society129(4): 267-381
^abMichelle van der Bank, Michael F. Fay, and Mark W. Chase (2002). "Molecular Phylogenetics of Thymelaeaceae with particular reference to African and Australian genera".Taxon51(2):329-339.
^abMarline Rautenbach. "Gnidia is not monophyletic: taxonomic implications for Gnidia and its relatives in Thymelaeoideae". Digispace at the University of Johannesburg 8 Jul 2008. (see External links below)
^abcdB.E. Herber. "Thymelaeaceae" In:The Families and Genera of Vascular Plants vol.V (Klaus Kubitzki and Clemens Bayer, volume editors). Springer-Verlag: Berlin, Heidelberg (2003)
^David Galicia-Herbada (2006). "Origin and diversification of Thymelaea (Thymelaeaceae): inferences from a phylogenetic study based on ITS (rDNA) sequences".Plant Systematics and Evolution257(3-4):159-187.
^Hutchinson, John.The Families of Flowering Plants, Third Edition (1973). Oxford University Press: London.
^Horn, J.W., (2004). "The morphology and relationships of the Sphaerosepalaceae(Malvales)".Botanical Journal of the Linnean Society144(1):1-40
^Klaus Kubitzki. "Tepuianthaceae" In:The Families and Genera of Vascular Plants, vol.V Klaus Kubitzki and Clemens Bayer. (volume editors). Springer-Verlag: Berlin, Heidelberg. (2003).
^Vernon H. Heywood, Richard K. Brummitt, Alastair Culham, and Ole Seberg.Flowering Plant Families of the World. Firefly Books: Ontario, Canada (2007)
^Marline Rautenbach. Figure 1.2, page 7 In: "Gnidia is not monophyletic: taxonomic implications for Gnidia and its relatives in Thymelaeoideae" Digispace at the University of Johannesburg. 8 Jul 2008. (see External links below).
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