Buxaceae

The Buxaceae (Buxaceae) are a family of angiosperm plants belonging to the order Buxales. It consists of five genera, with about a hundred species, distributed throughout the northern hemisphere, extending to the South American Andes, the Caribbean, South Africa, Madagascar and Southeast Asia.

Description

Pachysandra terminalis.

• Perennial trees or shrubs up to 15 m tall, rarely subarbustos or perennial rhizomatous herbs in Pachysandra. Indumento absent, sometimes with uni- or multicellular hairs of thick walls.
• Dorsiventral leaves, alternating or decused with decurrent bases that form internal folds, simple, whole (dented in Pachysandra), pecioladas (rarely seated), no stypules, nerviación pinnatinervia, seldom triplinervia, basically brochydodroma in tropical areas, in other cases eucamptódroma, cladodroma or craspedódroma, especially in subtropical and temperate areas. Epidermis foliar covered with cuticular waxes. Abaxial, laterocytic (occasionally cyclic) stomas, with very developed external reversals and a peristomal reversal at times. Mesophyl with prominent secretive cells, sometimes forming a continual hypodermis that includes various types of glare: brachyesclereides, osteoesclereides or astroesclereides.
• Simple rizomes, with adventitious roots, which develop simple stems or with sympathetic branching and leaves grouped in the ends. The branches present a cortical vascular beam at each angle in the species of Buxus and Notobuxus of the Old World, absent in others, accompanied by sclerenequimatous pods open or closed. Nodes unilacunares with a foliar trace (3 traces in Sarcocca).
• Single plants, seldom dioecious, more seldom even polygamodiac (with some perfect flower).
• Inflorescences in spike or racemiformes, axillary or terminals, in Pachysandra procumbens on the base of the stem, the male flowers above the female, or a female above the male, with decurrent basal bracts, the female bracteolates. In the dioecious species Styloceras, the male flowers form long ears with a pelric flower at the end and the female flowers are solitary or clustered in thorny.
• Actinomorphous, greenish, pituitary, absent hypoginal disco. Male flowers with bractéolas decused in the pedicelo, with 4 decused tepals, seldom absent, in two verticils of 2, androceo of 4 free stamens, antetepals, in 1-2 verticils, if there are 6 then two pairs opposite to the internal tepalos and a pair to the external ones, or 8-45 in complex arrangement, with the long Female flowers often greater than males but more rare or solitary, each with a pair of bracts and several spiral bracholes in the pedicel, sparsely differentiated from teapals, with 4-6 tepals, in two verticils of 2-3, super gynae, paracarpal, of 2-3(-4) carpals, sometimes with fake carpals separating Pachysandra and Styloceras), free styles (rarely soldiers at the base), subulates, divergents, more or less long and recurved, with nectariferous protuberances between the bases, large stigma, bilobed, obliquely decurrent by the inner fold of the styling, dry or slightly humid, papiloso, ovulos normally 2 per carpelle (se in unio segments Pachysandra), anthropists, collateral, pendulums, apotropes, bitégmicos, crasinucelados, placenta forming a shutter in Pachysandra, the external tegument proliferates giving a perinellary hood that becomes the seminal caruncula, axial placentation to apical. Absent stencils.
• Fruto dehiscente, in locliced capsule, with persistent stylings, the bicorns, or indehiscent, more or less similar to a drupe or berry.
• Seeds oblong, trigone, black, blond or shiny blue, often with caruncula, abundant endosperm, fleshy, oily, straight embryo to slightly curved, with 2 flat and thin cots.
• Pole in monads, spheroidal, between 20 and 50 μm in diameter, 3-7-colporate, 5-12-pantocolporate or 12-40-pantoporate, in Buxus each colpo internally with 3-6 pores (ora), decreasing the number of ora in the pantocolporate grains, the pores of rounded pantoporate grains, with sculpted membranes, exine of different forms, reticulate, spinulada, verrugosa or baculada, of great systematic interest.
• chromosomal number: x = 7; most species Buxus and Sarcocca They have 2n = 28, in Notobuxus registered 2n = 20, in Pachysandra known n = 12, 13, 24 and 27.

Ecology

Aspect Buxus sempervirens.

Some species of Buxus show occasional parthenocarpy, while some species of Sarcococca appear to be obligate apomictic. Pachysandra procumbens is self-compatible. In Sarcococca humilis the rare phenomenon of polyembryony occurs. Pollination is carried out by entomogamy, being the main agents bees and flies. The flowers are protogynous and nectar-bearing (especially the male ones), so the contact of the pollinators with the female flowers is simply casual due to their proximity to the male ones, due to their attraction due to their weak odor and the tepals, filaments and colored anthers. However, in African Buxus and Notobuxus there are no nectaries and it has been suggested that pollination is anemogamous, which is partly confirmed by the increased number of stamens. The seeds of the capsules are detached when they open and are dispersed by rain or water currents. The seeds with a caruncle present myrmecochory, while the drupe or berry fruits are dispersed by endozoochory, probably by birds that use them for food.

The species are found in a broad tropical to temperate belt in the Old and New Worlds, colonizing from shrubby xeric habitats to mesophytic or humid montane forests above 3000 m, coastal or low-lying forests.

Phytochemistry

Buxus sempervirens.

Steroidal alkaloids of the aminopregnane type present (as in Didymelaceae), of which about 150 different ones have been isolated, mainly derivatives of pregnane and irehdiamine, including buxin. absent iridoids. Proanthocyanidins present or absent. Saponins and sapogenins absent. Seventeen Cuban species of Buxus are nickel hyperaccumulators, reaching contents of 1-25 mg/g of dry weight.

Uses

In general, the family has a moderate economic interest. Boxwood species (Buxus spp.) are used in landscaping for hedges and topiary decoration. Its wood is used in turnery, furniture inlay, carving, engraving, instrumentation and tools. Pachysandra terminalis is used in gardens as a ground cover, as is Pachysandra procumbens. Sarcococca species are cultivated for their small, but intensely aromatic winter flowers. The wood of Styloceras is exploited for carpentry. The boiled shoots and leaves of Sarcococca saligna are applied in Pakistan to painful or swollen joints for healing.

Conservation

Sarcococca humilis.

The IUCN considers 7 species of Buxaceae to be threatened, of which one species from South Asia, Buxus vahlii, is in a critical situation. It is evident that the whole family is suffering a contraction of its area, much wider in past times, due, apparently, mainly to climatic changes.

Fossils

Fossil records of Spanomera from the Albian/Cenomanian Potomac Group are closely related to this family (98-113 Ma). Pollens attributable to it are initially known from the Late Cretaceous of central Europe and in the Paleogene records show an extension of the area first to the west and then to the east, reaching eastern Asia in the Miocene. Macrofossils of Pachysandra are recorded from the Upper Eocene of central Europe, and of Sarcococca from the Upper Oligocene/Miocene of the same area. Fossil pollens of Buxus are known from the Lower Eocene and fruits and leaves from the Miocene of Bohemia and the Oligocene of East Asia. Styloceras pollen has been found from the Eocene of Argentina and the Pliocene of Colombia. The origin of the family has been estimated possibly from 118-99 Ma ago.

Systematic position

The Buxaceae are a group of angiosperms that are included in the Eudicotyledonous clade. In previous systems, its position has been problematic, having been frequently associated with the Euphorbiaceae and also included in the Orders Celastrales, Hamamelidales and Pittosporales. Recent molecular analyses, along with new morphological data, have allowed it to be related to the Didymelaceae as its sister group, in the basal grade of the Eudicots, being recognized by the APW (Angiosperm Phylogeny Website) as a family of the Order Buxales (cf. AP-website). Some authors prefer to also include this last family in the Buxaceae. However, the current trend is to keep them separate due to their very different morphology, which would make a diagnosis of the family resulting from the merger difficult.

Taxa included

Theoretical Introduction in Taxonomy

Within the family, two monophyletic clades are recognized, resolved by both morphological and molecular analysis: the tribe Sarcococceae and the tribe Buxeae (Dumort., 1822) Dumort., 1829. The first includes a basal branch formed by Styloceras, which is the sister group of the clade formed by Sarcococca and Pachysandra, while the second This tribe includes Buxus and Notobuxus, but the latter appears immersed within the African representatives of the former, so the options are either to dismember Buxus or include Notobuxus in it, this last option being the one used by different authors (eg Hutchinson. In this treatment it is kept separate, following Köhler (2007, see reference).

The genera can be distinguished by using the following identification key:

Buxus sinica.

• Male flowers with absent teapals. Stamens 11-45.

Styloceras A. Juss, 1824. South America, especially in the Andes and adjacent areas.

• Male flowers usually with 4 teapals. Stamens 4-10.

• Alternate leaves. Female flowers at the base of the clusters or ears. Indehiscent fruit, dash or capsular.

• Busts or trees. Whole leaves. Fruit more or less dash.

Sarcocca Lindl, 1826. Southeast Asia.

• Perennial herbs of tracing stems. Sheets more or less dented. Sub-dirupted or capsular fruit.

Pachysandra Michx, 1803. East North America, China, Taiwan.

• Decused leaves. Terminal female flowers in racemiform inflorescences more or less condensed. Fruit dehiscent, in capsule.

• Male flowers with 4 oposititépalos stamens. Long stamina. Pistilodio present. 2n = 28, 56.

Buxus L., 1753. Central America, Caribbean, South Europe, North and South Africa, Madagascar, East Asia.

• Male flowers with 6(-10) stamens, two pairs opposed to internal teapals. Absent staminal filaments. Pistilodio a flat or absent disc. 2n = 40.

Notobuxus Oliv., 1882. Central and West Africa to South Africa.