keys to the vascular plants of east texas - Botanical Research ...

396 PINACEAE/PINUS
(Stahle et al. 1988; Stahle 1996). According to Briand and Soros (2001), the “function of cypress
knees has long intrigued botanists. In 1819, Michaux stated – ‘No cause can be assigned for their
existence.’, to which in 1882 Asa Gray concurred. Since the late 19th century a number of theories
have been put forward to explain their function, including aeration of the root system, vegetative
reproduction, mechanical support, nutrient accumulation and carbohydrate storage.
After nearly two hundred years of speculation and research, the function or functions of the
knees of the cypresses still remains unclear.” This species will grow in a variety of situations,
while wild plants are virtually always in wet areas, BALD-CYPRESS does extremely well as a
street tree and in lawns. It is currently being widely planted in East TX. Though often seen
growing in relatively shallow water considerable distances from the shore of lakes, the species
is reported to germinate only on moist but unflooded soil (Stalter 1981). g
Two other varieties deserve mention:
Taxodium distichum var. imbricatum (Nutt.) Croom, (overlapping in regular order like tiles), [T.
ascendens Brongniart, T. distichum var. nutans of authors, not (Aiton) Sweet—Watson 1985],
POND-CYPRESS, is native in the se U.S. from NC s to FL and w as far as e LA (Watson 1993). It can
be distinguished from var. distichum as follows: short shoots mostly ascending vertically; leaves
not 2-ranked, mostly narrowly lanceolate, ca. 3–10 mm long, appressed and overlapping, the
free portion neither contracted nor twisted basally (Watson 1993). While some authorities treat
this taxon as a separate species (e.g., Nauman 2000), we are following Watson (1993) who
treated it as a variety. Recent molecular evidence (Tsumura et al. 1999) supports recognition of
POND-CYPRESS at the varietal level.
Taxodium distichum var. mexicanum Gordon, (of Mexico), [T. mucronatum Ten.], MEXICAN or
MONTEZUMA BALD-CYPRESS, includes the famous “Tule Tree” of Oaxaca, one of the world’s largest
trees (in circumference) (Hall et al. 1990; Dorado et al. 1996; Debreczy & Rácz 1998). This � evergreen
variety extends as far n as s TX. According to Watson (1993), var. mexicanum exhibits
continuous morphologic intergradation with var. distichum and there is some question as to
whether it should be treated as a separate variety.
PINACEAE Spreng. ex F. Rudolphi
PINE FAMILY
AA primarily n hemisphere family of 10 genera and ca. 200 species (Thieret 1993). It is of
great economic importance as a source of softwood timber, pulpwood, naval stores (e.g., turpentine),
Christmas trees, and ornamentals. In addition to Pinus (PINE), important genera include
Abies (FIR), Picea (SPRUCE), Pseudotsuga (DOUGLAS FIR), and Tsuga (HEMLOCK). Pseudotsuga
menziesii (Mirbel) Franco, of w North America, with trunks 3–4 m in diam. and over 90 m tall,
is one of the most important lumber trees in the world (Lipscomb 1993; Woodland 1997); an individual
133 m tall was reported to have been felled in British Columbia in 1895 (Mabberley 1987).
It is frequently sold as a Christmas tree in East TX and can be recognized by the pointed buds.
FAMILY RECOGNITION IN THE FIELD: trees with long, needle-like leaves in bundles of 2 or 3 (East
TX species) and large woody cones; tissues resinous and aromatic.
REFERENCES: Dallimore & Jackson 1931; Correll 1966b; Little 1971; Price 1989; Farjon 1990a,
1990b; Page 1990c; Thieret 1993.
PINUS L. PINE
Monoecious (pollen cones and seed cones on the same tree), evergreen, resinous, aromatic trees
to 30 m or more tall; leaves of 2 kinds: scale-like leaves subtending minute branchlets, each
branchlet bearing a fascicle of 2–3 (in East TX species) elongate, needle-like foliage leaves
(= needles) surrounded at the base by a membranous sheath; staminate (pollen) cones small, in