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Turnera
diffusa Willd. ex Schult.
Standardized Common
Name: Damiana
Family: Turneraceae
Taxonomy: The genus includes
about 100 species, almost all native to the New World, which are divided into 9
series. Turnera diffusa belongs to Ser. Microphyllae Urb., which
is characterized by small leaves with stipules fused to the petiole, a pleasant
smell produced by glandular hairs, a lack of extrafloral nectaries, and a suite
of reproductive characters (e.g., sessile axillary flowers and warty fruits).
Two varieties of T. diffusa are recognized: the commoner var. diffusa
is widely dispersed from Texas and southern California through Central America
and the Caribbean, with disjunct populations in eastern Brazil, whereas var. aphrodisiaca
(Ward) Urb. is confined to Central America, Cuba and Haiti. Frequently
encountered synonyms include T. aphrodisiaca Ward and T. microphylla
Desv.
Description: Shrub or subshrub to
2 m high, erect to sprawling. Stems frequently branching, reddish brown to
yellowish, with prominent leaf scars. Leaves alternate or clustered, sessile or
short-petiolate, stipulate with stipules <1 mm long; blade (2–)5–38(–50) mm
long, (1–)2–15(–19) mm broad, narrowly obovate or oblong to narrowly ovate;
base cuneate to attenuate or spatulate; apex obtuse; margins crenate and
revolute; venation pinnate, prominent beneath; upper surface olive to dark
green, lower surface paler; pubescence variable especially on lower surface,
from nearly glabrous to densely pubescent and glandular. Flowers axillary, solitary,
subsessile, subtended by 2 bracts; bracts 2.5–7 mm long, variable in shape,
entire or weakly toothed, sometimes pubescent and bearing glands. Calyx 3–8 mm
long, tubular with 5 long, 3-nerved teeth, pubescent on both surfaces. Petals
yellow or rarely whitish, 4–7(–9) mm long, obovate, the base narrowed and
sometimes pubescent. Stamens 5, with filaments somewhat flattened near base;
stamens longer than styles in some flowers, shorter in others. Ovary
unilocular; styles 3, pubescent or glabrous. Fruit a capsule, 2.5–4.5 mm long,
ovoid, 3-valved, warty and pubescent above with glandular hairs; seeds curved,
dark, bearing small angular pits in longitudinal rows.
Parts
in commerce:
Leaves
Identification:
- Oblong to
narrowly obovate or narrowly ovate
- 0.5–4(–5) cm
long
- Base tapering,
with or without a distinct short (<7 mm) petiole
- Apex obtuse
- Margins revolute
and bearing a few, often somewhat rounded teeth
- Venation
pinnate; secondary veins parallel, leaving midrib at 45–60º angle and
running towards notches between teeth, usually splitting before the notch
- Secondary veins
sunken on upper surface, prominent on lower surface
- Upper surface
olive to dark or pale green, sometimes discolored, glabrous to pubescent
- Lower surface
paler, frequently grayish to whitish, nearly glabrous to pubescent;
pubescence quite variable, sometimes present only over veins, sometimes
dense
- Glandular hairs
on lower surface yellowish or whitish, stalkless
- Odor aromatic
- Taste aromatic,
pleasant
Adulterants: Isocoma veneta
(Kunth) E. Greene, formerly known as Aplopappus or Haplopappus
discoideus DC., a member of the aster family, was frequently reported as an
adulterant in the past. Its leaves differ from those of T. diffusa in
several features:
- Teeth fewer,
mostly toward apex, sharply pointed
- Margins not
revolute
- Apex acute
- Tapering basal
portion of leaf proportionately longer, to over half the length of the
blade
- Glandular dots
black
- Secondary veins
inconspicuous
- Odor and taste
resinous or balsam-like
It
has been stated in at least one pharmacognostic text that Damiana leaves are
10–25 cm long; this measurement (if not a misprint) must have been derived from
leaves of some other species, as leaves of T. diffusa never approach 10
cm in length.
References:
Arbo MM. Estudios sistemáticos en Turnera (Turneraceae)
II. Series Annulares, Capitatae, Microphyllae y Papilliferae. Bonplandia.
2000;10:1–82.
British Herbal Medicine
Association. British Herbal Pharmacopoeia. BHMA; 1996:67–68.
Evans WC. Trease and Evans’ Pharmacognosy, 14th ed. London: WB Saunders
Company Ltd.; 1996:290.
Youngken HW. Text-Book of Pharmacognosy, 5th ed. Philadelphia, PA: The
Blakiston Company; 1943:587–588.
Figure 79: a–b, Turnera diffusa leaf and close-up.
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