Neotropical Buxaceae

Egon Köhler

Humboldt Universität zu Berlin, Germany. 

Description

Evergreen shrubs, trees (to 15 m tall). Stipules absent. Leaves alternate (Styloceras Kunth ex A.Juss.and Sarcococca Lindl.) or decussate (Buxus L.), simple, petiolate, rarely sessile, blades with bases decurrent as internodial folds on the branchlets (Buxus), margins entire, venation pinnate, less often ± tripli-veined. Inflorescences axillary, less frequent terminal, racemes, clusters, or spikes, sometimes of solitary pistillate flowers (Styloceras), the racemes loose to densely glomerate, with single apical female flower  (Buxus), the clusters or spikes often erect with apical staminate flowers (Sarcococca), these sometimes pendent (Styloceras), the flowers subtended by bracts and bracteoles (Sarcococca). Flowers actinomorphic, unisexual, plants monoecious or dioecious (some Styloceras), small. Staminate flowers: tepals 2+2, inconspicuous, bract-like or sometimes petal -like or lacking (Styloceras); petals absent; androecium usually with 4 stamens, opposite the tepals, or stamens numerous (Styloceras), inserted on angular-ovate bracts, the stamens usually inserted around a pistillode, nectariferous (lacking in Styloceras), anthers dorsifixed to basifixed, tetrasporangiate, longitudinally dehiscent, with protruding connective tip. Pistillate flowers: tepals 4-6, bract-like; petals absent; gynoecium syncarpous, the ovary superior, the carpels (2-)3(-4) with free, sometimes large divergent styles (Styloceras), rarely connate at the base, persistent on fruit (Buxus), the stigma decurrent along the ventral fold, nectariferous protuberances occuring between styles (Buxus, possibly of androecial origin); the locules (2-)3(-4), sometimes with false septa, divided into uni-ovulate locelli (Styloceras and Pachysandra Michx.); placentation axile; ovules usually 2 per locule, pendent, anatropous, bitegmic. Fruits capsules (Buxus), drupe-like (Sarcococca and Styloceras); capsules dehiscing loculicidally into 3 spreading, 2-horned valves, the exocarp chartaceous, the detaching endocarp cartilaginous, partly enclosing and ejecting the seeds; drupaceous fruits with a pulpy mesocarp and a thin crustaceous or cartilaginous endocarp, divided in 4-6 pyrenes (Styloceras). Seeds usually (2-)4-6 black or blue, shining, caruncle present (Buxus); endosperm copious, fleshy, oily, the cotyledons thin, flat.

Notes on delimitation

  • The family comprises two subfamilies, the Buxoideae and Styloceratoideae, supported by recent molecular data as two major clades.
  • Styloceras is sometimes regarded as a separate family, and is recognized as a sister group of Sarcococca and Pachysandra.
  • The rank of Notobuxus Oliv. is still in discussion. It was recently treated as a subgenus of Buxus, but deviates in the number of stamens, the chromosome number, and features of the exine.
  • The family has frequently been associated with Euphorbiaceae, but Celastrales and Hamamelidales have also been considered.
  • Recent morphological and molecular data place Buxaceae as sister to Didymelaceae (Buxales) together with Ranunculales, Sabiaceae, Proteales and Trochodendraceae in a grade at the base of the eudicots.

Distribution in the Neotropics

  • Buxus - Mexico, Mesoamerica, Caribbean, Caribbean coast of northern South America.
  • Sarcococca - southern Mexico, Guatemala (1 species, generic position doubtful, Sealy 1986).
  • Styloceras - Andean South America, Bolivia, Ecuador, Peru, Venezuela.

Distinguishing characters (always present)

Other important characters

  • Stamens 4, opposite the tepals.

OR

  • Stamens numerous, then tepals wanting.

Number of genera

5 genera worldwide (3 in Neotropics)

  • Buxus
  • Notobuxus
  • Pachysandra
  • Sarcococca
  • Styloceras

Useful tips for generic identification

Key to genera of Neotropical Buxaceae

1. Tepals absent, male flowers in pendent spikes, stamens numerous, inserted on bracts, ovary 2(3)carpellate ...Styloceras
1. Tepals present, stamens usually four ... 2

2. Leaves decussate, female flowers terminal in racemes or clusters, fruit a 3-valved capsule...Buxus
2. Leaves alternate, female flowers, normally at base of racemes, in the Neotropics as uppermost, fruit subdrupaceous ...Sarcococca

Notable genera and distinguishing features

Buxus:

  • Tetragonal branchlets.
  • Leaves decussate.
  • Flowers in lax to glomerate racemes with a terminal female flower.
  • Staminate 4-merous tepals and stamens.
  • Tepals decussate.
  • Stamens opposite tepals, inserted around a pistillode.
  • Fruit a 3-horned capsule.
  • Dehiscing loculicidally into 3 spreading 2-horned valves.

Sarcococca

Styloceras:

Status

  • Styloceras is endemic to South America.
  • Buxus has native representatives in the Neotropics.
  • Sarcococca is a mainly East Asian genus with 1 species in Guatemala and Mexico, still of doubtful generic affiliation.

General notes

  • The family has a disjunct intercontinental distribution with centers of diversity in tropical and temperate East Asia and in the Caribbean.
  • In the Western Hemisphere the family is distributed from south-eastern United States (one species of Pachysandra) to Andean South America (five species of Styloceras) and the Caribbean coast of northern South America.
  • One species of Sarcococca is recorded from Guatemala and southern Mexico.
  • The largest and most widespread genus, Buxus, has a marked center of diversity in Cuba.
  • The genus Buxus is economically important for its horticultural value. More than 150 registered cultivars, mainly of B. sempervirens L. and B. microphylla Sieb. & Zucc., are used for edging, for pruning and for topiary work. The closely grained wood is employed for turning, engraving and manufacturing musical instruments.
  • Styloceras provides first class timber for joinery.

Important literature

Balthazar, M. von & Endress, P.K. 2002. Reproductive structures and systematics of Buxaceae. Bot. J. Linn. Soc. 140:193-228.

Balthazar, M. von & Endress, P.K. 2002. Development of inflorescences and flowers in Buxaceae and the problem of perianth interpretation. Intl.J.Pl.Sci. 163:847-876.

Balthazar, M. von, Endress, P.K. & Qiu, Y.-L. 2000. Phylogenetic relationships in Buxaceae based on nuclear internal transcribed spacers and plastid ndhF sequences. Intl.J.Pl.Sci. 161:785-792.

Batdorf, L.R. 2005. Boxwood Handbook. Boyce: American Boxwood Society.

Gentry, A.H. & Foster,R. 1981. A new Peruvian Styloceras (Buxaceae): discovery of a phytogeographical missing link. Ann. Missouri Bot. Gard. 68:122-124.

Gentry, A.H. & Aymard, G. 1993. A new species of Styloceras (Buxaceae) from Peru. Novon 3:142-144.

Köhler, E. 1981. Pollen Morphology of the West-Indian-Central American species of the Genus Buxus L. (Buxaceae) with reference to taxonomy. Pollen et Spores 23:37-91.

Köhler, E. 1993. Blattnervatur-Muster der Buxaceae Dumortier und Simmondsiaceae van Tieghem. Feddes Repertorium 104:145-167.

Köhler, E. & Brückner, P. 1990. Considerations on the evolution and chorogenesis of the genus Buxus (Buxaceae). Mem. New York Bot. Gard. 55:153-168.

Köhler, E., Fernández, R. & Zamudio, S. 1993. Buxus moctezumae Köhler, Fernández & Zamudio (Buxaceae) una especie nueva de Estado de Querétero, México. Feddes Repertorium 104:295-305.

Köhler, E. 2004. Buxaceae. In: N.Smith, S.A.Mori, A.Henderson. D.W.Stevenson & S.V.Head (eds.), Flowering Plants of the Neotropics: 70-72. Princeton, Princeton University Press.

Köhler, E. 2006. Three new Buxus species (Buxaceae) from eastern Cuba. Willdenowia 36: 479-489.

Mathou, Th. 1940. Recherches sur le famille des Buxacées. Toulouse:Douladoure.

Sealy, J.R. 1986. A revision of the genus Sarcococca (Buxaceae). Bot. J. Linn. Soc.92: 117-159.

How to cite

Köhler, E. (2009). Neotropical Buxaceae. In: Milliken, W., Klitgård, B. & Baracat, A. (2009 onwards), Neotropikey - Interactive key and information resources for flowering plants of the Neotropics. http://www.kew.org/science/tropamerica/neotropikey/families/Buxaceae.htm.