The Thymelaeaceae are a cosmopolitan family of flowering plants composed of 50 genera (listed below) and 898 species.Zachary S. Rogers (2009 onwards). A World Checklist of Thymelaeaceae (version 1). Missouri Botanical Garden Website, St. Louis. It was established in 1789 by Antoine Laurent de Jussieu.Antoine Laurent de Jussieu Genera Plantarum, page 76. Herrisant & Barrois, Paris. The Thymelaeaceae are mostly trees and shrubs, with a few vines and herbaceous plants, the latter including some annual species.
Description Several conspicuous or unusual traits are characteristic of the family (when Tepuianthus is excluded). The bark is usually shiny and fibrous, with strips of bark peeling down the side of broken stems.Ernst Schmidt, Mervyn Lotter and Warren McCleland The number of stamens is usually once or twice the number of calyx lobes; when twice, they often occur in two well separated series. Exceptions include Gonystylus, which may have up to 100 stamens, and Pimelea, which has only 1 or 2.
Thymelaeaceae are often difficult to identify because of equivocal interpretation of the flower parts. Sepals, petals, and staminodes are hard to distinguish, and many keys are ambiguous about whether staminodes should be counted as stamens. Moreover, in Wikstroemia, individual plants often produce anomalous flowers.
Taxonomy The family is named from the genus Thymelaea, the name of which is a combination of the Greek name for the herb thyme θύμος (thúmos) and that for the olive ἐλαία (elaía)—in reference to its thyme-like foliage (i.e. minuscule leaves) and olive-like fruit.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.
Classification The Thymelaeaceae are in the order Malvales.Peter F. Stevens (2001 onwards) Angiosperm Phylogeny Website In: Missouri Botanical Garden Website Except for a sister relationship with Tepuianthaceae, little is known for sure about their relationships with the other families in the order.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 Society 129(4): 267-381
Unlike most recent authors, who accept four subfamilies, B. E. Herber has divided Thymelaeaceae into two subfamilies. 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 to tribal 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, no subtribes were designated in the tribe Daphneae, but it was informally divided into four groups: the Linostoma group, the Daphne group, the Phaleria group, and the Gnidia group. The 45 genera accepted by Herber are grouped as follows. Three genera in Daphneae were placed incertae sedis (not assigned to any particular group or in a separate group by themselves).
Octolepidoideae Octolepis group: Arnhemia, Deltaria, Lethedon, Octolepis, Solmsia Gonystylus group: Aetoxylon, Amyxa, Gonystylus
Thymelaeoideae Synandrodaphneae: Synandrodaphne Aquilarieae: Aquilaria, Gyrinops Daphneae
Linostoma group: Craterosiphon, Dicranolepis, Enkleia, Jedda, Linostoma, Lophostoma, Synaptolepis Phaleria group: Peddiea, Phaleria Daphne group: Daphne, Daphnopsis, Diarthron, Dirca, Edgeworthia, Funifera, Goodallia, Lagetta, Ovidia, Rhamnoneuron, Schoenobiblus, Stellera, Thymelaea, Wikstroemia Gnidia group: Dais, Drapetes, Gnidia, Kelleria, Lachnaea, Passerina, Pimelea, Struthiola Incertae sedis: Linodendron, Stephanodaphne, Lasiadenia
Phylogeny The first molecular phylogeny for Thymelaeaceae was published in 2002. It was based on two regions of chloroplast DNA. These were the rbcL gene and the intergenic spacer between the transfer RNA genes trnL and trnF. 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 the Gnidia 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 and trnL-F data, sequences of the ITS (internal transcribed spacer) region of nrDNA (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 of Gnidia were chosen from among the most common or well known species in a way that shows which clades contain species of Gnidia.
Defining the genera
The circumscription of genera in Thymelaeaceae has always been difficult, and is to some degree artificial. For example, the difficulty of distinguishing Daphne from Wikstroemia has been commented upon by Rautenbach and Herber. Several small genera are probably embedded in Daphne or Wikstroemia, or if Daphne and Wikstroemia are intermingled, these small genera might be embedded in both simultaneously. Stellera, for example, is nested within Wikstroemia, at least (see the phylogenetic tree below).
A recent comparison of DNA sequences has established the monophyly of Thymelaea and the polyphyly of Diarthron,David Galicia-Herbada (2006). "Origin and diversification of Thymelaea (Thymelaeaceae): inferences from a phylogenetic study based on ITS (rDNA) sequences". Plant Systematics and Evolution 257(3-4):159-187. but there was not sufficient sampling in Wikstroemia and Daphne to exclude the possibility that Thymelaea, Diarthron, and others might be embedded in them.
The large genus Gnidia is polyphyletic and its species fall into four separate clades, each of which contains other genera of the family (see the phylogenetic tree below). The type species for Gnidia is Gnidia pinifolia. If Gnidia is divided into four or more separate genera, the segregate genus which contains G. pinifolia will retain the name Gnidia. Zachary S. Rogers published a revision of the Gnidia of Madagascar in 2009 in Annals of the Missouri Botanical Garden.
Some of the older treatments of Thymelaeaceae treat Lasiosiphon as a separate genus from Gnidia. This distinction was later shown to be artificial. However, Van der Bank et al. (2002)Michelle van der Bank, Michael F. Fay, and Mark W. Chase (2002). "Molecular Phylogenetics of Thymelaeaceae with particular reference to African and Australian genera". Taxon 51(2):329-339. suggested that Lasiosiphon might be resurrected if redefined. The type species for Lasiosiphon is Gnidia glauca, formerly known as Lasiosiphon glaucus.
Open questions
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 that Dais was found to be sister to Phaleria. The phylogeny casts significant doubt upon the monophyly of the subfamily Octolepidoideae, and upon the monophyly of the informal Octolepis and Gonostylus 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 and Peddiea might need to be transferred to the Gnidia group, but support was not strong (60% BP) for a clade consisting of the Gnidia group with Stephanodaphne and Peddiea. Again, more extensive sampling will be required to resolve this question. Two of the three genera placed incertae sedis by Herber (Linodendron and Lasiadenia) have not yet been sampled and their relationships to other genera remain obscure.
Genera
Herber (2003)B.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) accepts 45 genera, excluding Tepuianthus from the family, sinking Atemnosiphon and Englerodaphne into Gnidia, Eriosolena into Daphne, and Thecanthes into Pimelea. The largest genera and the approximate number of species in each are Gnidia (160), Pimelea (110), Daphne (95), Wikstroemia (70), Daphnopsis (65), Struthiola (35), Lachnaea (30), Thymelaea (30), Phaleria (30), and Gonystylus (25).
, Plants of the World Online accepts 52 genera.
Aetoxylon Amyxa Aquilaria Arnhemia Atemnosiphon Craterosiphon Dais Daphne Daphnimorpha Daphnopsis Deltaria Diarthron Dicranolepis Dirca Drapetes Edgeworthia Englerodaphne Enkleia Eriosolena Funifera Gnidia Gonystylus Goodallia Gyrinops Jedda Kelleria Lachnaea Lagetta Lasiadenia Lethedon Linodendron Linostoma Lophostoma Octolepis Ovidia Passerina Peddiea Phaleria Pimelea Restella Rhamnoneuron Schoenobiblus Solmsia Stellera Stephanodaphne Struthiola Synandrodaphne Synaptolepis Tepuianthus Thymelaea Wikstroemia
In the past, different authors have defined Thymelaeaceae in different ways. For example, John Hutchinson excluded Gonystylus and its close relatives, as well as Aquilaria and its close relatives from the family, forming two segregate families, Gonystylaceae and Aquilariaceae.Hutchinson, John. The Families of Flowering Plants, Third Edition (1973). Oxford University Press: London. But today, the only controversy that still remains over the circumscription of the family is the question of whether Tepuianthus should be included, or segregated as a separate, monogeneric family.Horn, J.W., (2004). "The morphology and relationships of the Sphaerosepalaceae(Malvales)". Botanical Journal of the Linnean Society 144(1):1-40 Stevens includes Tepuianthus, but Kubitzki treats Tepuianthaceae as a separate family.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).
Distribution The family is more diverse in the Southern Hemisphere than in the Northern, with major concentrations of species in Africa and Australia.Vernon H. Heywood, Richard K. Brummitt, Alastair Culham, and Ole Seberg. Flowering Plant Families of the World. Firefly Books: Ontario, Canada (2007) The genera are overwhelmingly African.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).
Ethnobotany and economic use