Thymelaceae

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.

Description

This is not intended as a full botanical description, but only as a few notes on some of the conspicuous or unusual traits of the family when ''Tepuianthus'' is excluded. The bark is usually shiny and fibrous. Attempts to break the stem often result in a strip of bark peeling down the side.Ernst Schmidt, Mervyn Lotter and Warren McCleland The number of stamens is usually once or twice the number of calyx lobes. If twice, then 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. The floral tube appears to be a calyx or corolla, but is actually a hollow receptacle. This feature is probably unique to Thymelaeaceae. The sepals are mounted on the rim of the floral tube. Stamens may be mounted on the rim or inside. What appear to be petals are actually stipular appendages of the sepals. The fruit is a 1-seeded berry or an achene. The 1-seeded berries have often been mistaken for drupes whenever the seed coat was mistaken for an endocarp.

When using a key to the families of flowering plants, Thymelaeaceae are often difficult or impossible to recognize 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.Warren L. Wagner, Derral R. Herbst, and Sy H. Sohmer. ''Manual of the Flowering Plants of Hawaii'', Revised Edition, 1999. Bishop Museum Press: Hololulu In these, the nonfunctional organs are much deformed and bear little resemblance to the parts that they represent.

A good collection of pictures of plants in this family has appeared in a scientific paper.

Taxonomy

The family is named for 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.

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 recognize 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 recognized 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 2 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 especially 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 4 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 4 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 recognize ''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 3 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) recognized 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).

, 50+ genera are accepted by the World Checklist of Thymelaceae:

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 2 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

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 are controlled by CITES. Many genera have inner bark yielding strong fibre suitable for the making of cordage and paper - a fact actually acknowledged in the naming of one of the genera, '' Funifera'' being the Latin for "bearer (provider) of rope". The barks of '' Daphne'', ''Edgeworthia'', '' Rhamnoneuron'', ''Thymelaea'', ''Stellera'', and ''Wikstroemia'' are used in paper-making, while '' Lagetta'' species are known as lacebark for their lacelike inner bark, the attractive appearance of which has led to their being used to make clothing and other utilitarian objects.

Toxicity and medicinal uses

Many of the species (e.g. ''Wikstroemia indica'' and ''Stellera chamaejasme'') have actual or potential uses in medicine and are poisonous if eaten, acting as violent purges (e.g. ''Daphne mezereum''), this toxicity often being related to the plants' containing phorbol esters which, as the name suggests, are also common in the spurge family Euphorbiaceae.

Use as ornamental plants

'' Daphne'' is grown (despite the high toxicity of its attractive fruits) for its sweetly scented flowers. Species of ''Wikstroemia'', '' Daphne'', ''Phaleria'', '' Dais'', ''Pimelea'' and other genera are grown as ornamentals.George W. Staples and Derral R. Herbst. 2005. "A Tropical Garden Flora". Bishop Museum Press: Honolulu. .Marline 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)

Gallery

File:Strettle Road Reserve pimelea.jpg, Inflorescence of the Australian ''Pimelea spectabilis''.
File:Daphne striata 100604.jpg, ''Daphne striata'', native to the Alps and the Dolomites.
File:Struthiola myrsinites Gonnabos IMG 1983s.jpg, The South African '' Struthiola myrsinites''.
File:Passerina (Thymelaeaceae) details of flowering sprig EOS 009.jpg, Flowers of an unidentified '' Passerina'' species.
File:Hortus Botanicus Leiden - Phaleria capitata Jack (Sumatra).JPG, '' Phaleria capitata'' of Sumatra exhibiting cauliflory.
File:Stellera chamaejasme 2.jpg, ''Stellera chamaejasme'' of Central and East Asia.
File:Daphnopsis racemosa Griseb. (12751985583).jpg, The Brazilian ''Daphnopsis racemosa'' in flower.
File:Daphnopsis racemosa Griseb. (17144500699).jpg, Fruits of ''Daphnopsis racemosa''.
File:Dirca palustris - Edwards.jpg, Flowers of '' Dirca palustris'' of the US
File:Akabana-mitsumata.JPG, '' Edgeworthia chrysantha'', native to China.
File:Wikstroemia phillyreifolia (Hawai'i false ohelo) flowers (6592426883).jpg, Flowers of the Hawaiian '' Wikstroemia phillyreifolia''.

References

External links

* Zachary S. Rogers (2009 onwards)
A Worldwide Checklist of Thymelaeaceae (version 1).


Peter F. Stevens (2001 onwards) In
Missouri Botanical Garden

Rautenbach(2008)
in
UJDigiSpace @ The University of Johannesburg

distribution
in: Gnidia is not monophyletic: taxonomic implications for Gnidia and its relatives in Thymelaeoideae
Thymelaeaceae of Mongolia in FloraGREIF

{{Taxonbar, from=Q156109

Malvales families