African cypress, Endlicher 1842
Cupressaceae

Widdringtonia - African cypress description

Evergreen trees and large shrubs with a dense branching habit. Trunk single or often dividing near the base, clothed with fibrous bark that peels in scales and strips. Twigs all more or less alike, without clear differentiation into long and short shoots, although strong and leading shoots are thicker and have longer leaf spacing than others, branching in three dimensions. Resting buds unspecialized, without distinct bud scales and consisting solely of as yet undeveloped ordinary foliage leaves. Leaves in alternating similar pairs, without differentiation into lateral and facial pairs, or irregularly spiral in youth. Juvenile leaves needlelike, linear, flat, sometimes persisting into, or present as reversions during, the adult phase. Adult leaves scalelike, the attached bases completely clothing the twigs, the free tips pressed against or standing out from the twigs, living 2-4 years.

Plants monoecious. Pollen cones scattered, not stalked, single at the ends of short lateral twigs, seated directly between a pair of foliage leaves without transitional pairs of bracts. Individual cones ellipsoid, with four to seven alternating pairs of pollen scales. Each scale usually with four pollen sacs arrayed along the lower edge of the inverted-heart-shaped, upturned blade. Pollen grains small (20-30 µm in diameter), roughly spherical and with an almost featureless surface. Seed cones single or clustered at the ends of short, stout axillary branchlets, maturing in two or three seasons and then remaining unopened for several years. Individual cones almost spherical before opening, normally with two nearly equal pairs of thick woody scales attached basally around a broad central bump (the columella), the inner (upper) pair meeting in a straight line at the center so that the members of the outer (lower) pair do not touch. Each cone scale flattened or convex externally, the boundary between the fully jointed bract and seed scale portions scarcely recognizable (in part because of extreme reduction of the seed scale), with a more or less prominent point or knob near the upper margin and with 1-8(-15) seeds in one or two rows at the base. Seeds angular, two-winged, the wing an outgrowth of the seed coat. Cotyledons two (or three), each with one vein. Chromosome base number x = 11.

Wood often powerfully fragrant, light to moderately heavy and soft to moderately hard, highly decay resistant but extremely flammable, shiny, the narrow band of whitish to yellowish sapwood scarcely distinguishable from to sharply contrasting with the yellow or pale reddish to light brown heartwood. Grain even and fine to moderately coarse, with ill-defined to obvious growth rings marked by a gradual transition to a narrow band of smaller but often not notably thicker walled latewood tracheids. Without resin canals but with numerous individual resin parenchyma cells scattered through the growth increments with some concentrated into open bands.

Stomates scattered or in irregular lines across the exposed surface of the leaf tips and in one or a few lines on the hidden face and extending sparingly into the grooves between the attached leaf bases. Each stomate sunken beneath and partly hidden by the (four or) five (or six) surrounding subsidiary cells, which are surmounted by a lobed, complete, steep Florin ring that stands atop the very thick cuticle covering all of the epidermal cells, some of the rest of which have additional, thickened, knoblike papillae. Midvein single, remaining close to the twig axis in the leaf base and soon petering out in the free tip, accompanied toward the outside (lower side) by a large resin canal and often flanked by two smaller ones beyond the large accompanying wedges of transfusion tissue. Photosynthetic tissue with a prominent, partially doubled palisade layer over the whole outer face of the leaves (except beneath the stomates) directly beneath the epidermis without an intervening hypodermis (or with a partial and incomplete one), the remaining, looser spongy mesophyll dotted with individual large resin cells.

Four species in southern Africa from the Cape of Good Hope, South Africa, to Malawi. Three of the species are very local, while the fourth occupies almost the entire range of the genus. All four occur in fire-prone habitats and require fire for natural regeneration. They also all possess fragrant, highly resinous wood that is resistant to decay but also resistant to paint. The three local ones were important sources of timber before they were depleted, while the single widespread species, Widdringtonia nodiflora, rarely reaches commercial size. Since species of the genus are not very hardly and are hardly cultivated outside of botanical gardens and tree collections, it is not surprising that there has been no cultivar selection as yet.

The name of the genus honors British Naval Commander Samuel Edward Widdrington (1787 – 1856). He had no direct connection to these trees, but in 1842 he published the last of three articles on European Pinus and Abies species just as Endlicher searched for a new name for the genus because two previously proposed names (one by him to replace an earlier one by Brongniart) had each been scooped in the year before it was proposed for an entirely different plant (1833 versus 1832, and 1844 versus 1840). There may have been a tinge or irony in this choice because Widdrington himself had just changed his own name (in 1840), the two previous articles having been published in 1839 under his birth name, Cook.

Widdringtonia is the only member of the southern hemisphere cypress subfamily Callitroideae native to Africa. It was long thought to be closely related to the superficially similar Tetraclinis in North Africa, but a closer look at their structures and DNA studies show that the latter is unrelated and, instead, belongs with other genera in the northern hemisphere subfamily Cupressoideae. Seed cones of Tetraclinis lack the central columella that links Widdringtonia to the cypress pine (Callitris) of Australia and related genera. In fact, Widdringtonia is closest to the Tasmanian subalpine shrub Diselma, which has similarly constructed but much smaller seed cones less than 5 mm long (versus more than 1 cm, usually much more, in Widdringtonia). The other related genera all have leaves and cone scales in threes or fours rather than in pairs. Rare individuals of Widdringtonia may also have parts in threes as an aberration, just as opposite-leaved flowering plants sometimes do. Among conifers, several junipers (Juniperus), like Widdringtonia members of the Cupressaceae, take this variability further and commonly show both conditions.

Peculiarly, given its relationships, there is no fossil record of Widdringtonia in the southern hemisphere. Instead, remains attributed to this genus were widely distributed around the North Atlantic (eastern North America, Greenland, and Europe) during the middle of the Cretaceous, from about 95 million years ago, and persisted into the mid-Tertiary (Oligocene, ca. 30 million years ago) in Europe. These fossils are, indeed, very like living Widdringtonia species, although the seed cones are generally smaller, so their northern location and age (older than most records of still extant conifer genera), combined with the phylogenetic nesting of the genus firmly among the purely southern genera of subfamily Callitroideae, are puzzling and worthy of further investigation.

References

• Farjon, A. (2010). A Handbook of the World's Conifers. Koninklijke Brill, Leiden.
• Eckenwalder, J.E. (2009) Conifers of the World: The Complete Reference. Timber Press, Portland.
• IUCN Red List of Threatened Species, International Union for Conservation of Nature and Natural Resources. Cambridge, UK /Gland, Switzerland

Copyright © Aljos Farjon, James E. Eckenwalder, IUCN, Conifers Garden. All rights reserved.