Flora of North America species comparison

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Triadenum

marsh, marsh St. John's wort
Habit Herbs, perennial, rhizomatous, glabrous, with glandular canals, lacunae, or dots containing essential oils (pale) in various parts and, sometimes, reddish to purplish gland dots containing hypericin on stems and leaves.
Stems

internodes with 2 or 4 raised lines at first, then terete (not lined).
Leaves

sessile, subsessile, or petiolate;

blade relatively broad, venation pinnate, tertiary veins densely reticulate, glands punctiform, pale (records of black gland dots are probably all due to fungal attack), intramarginal and laminar.
Inflorescences

terminal, sometimes also axillary, cymose, 2–15-flowered, or solitary flower, branching dichasial;

bracts and bracteoles relatively small.
Flowers

tubular or campanulate at first, expanding to stellate for short time each day;

sepals persistent, 5, distinct or almost so, margins not glandular-ciliate;

petals deciduous, 5, partly imbricate or contorted, pink or flesh-colored, sometimes green-tinged;

stamens persistent, 9, in 3 fascicles, each with 3 stamens;

filaments of each fascicle 1/5–1/2+ connate;

anthers yellow, isodiametric to oblate or shortly oblong, with amber gland on connective;

staminode fascicles 3, alternating with stamen fascicles;

ovary 3-merous;

placentation axile;

ovules relatively numerous on each placenta;

styles distinct, spreading.
Capsules

3-valved, with glandular vittae.
Seeds

narrowly cylindric, carinate;

testa reticulate-foveolate.
x

= 19.

Triadenum
Distribution
from USDA
e North America; Asia (e China, India [Assam], Japan, Korea, e Siberia, Taiwan)
Discussion

Nomenclatural complexities and confusions associated with Triadenum were reviewed by N. K. B. Robson (1977). B. R. Ruhfel et al. (2011) concluded from molecular studies that Triadenum is part of Hypericum. Robson (2012) gave reasons why Triadenum is generically distinct.

Species 6 (4 in the flora).

(Discussion copyrighted by Flora of North America; reprinted with permission.)
Key
1. Leaves petiolate.
T. walteri
1. Leaves sessile or (distal) subsessile
→ 2
2. Leaves: gland dots intramarginal.
T. tubulosum
2. Leaves: gland dots laminar and intramarginal
→ 3
3. Sepals 4–7(–8) mm, apex acute to acuminate; styles 2–3.5 mm.
T. virginicum
3. Sepals 2.5–5 mm, apex usually obtuse to rounded, rarely acute; styles 0.5–1.5 mm.
T. fraseri
Source FNA vol. 6, p. 102.
Parent taxa Hypericaceae
Subordinate taxa
T. fraseri, T. tubulosum, T. virginicum, T. walteri
Synonyms Gardenia, Hypericum section Elodea
Name authority Rafinesque: Fl. Tellur. 3: 78. (1837)
Web links 
Unless otherwise noted, all data comes from the online version of the Flora of North America, who have made most of their content available via a Creative Commons license (CC BY 4.0).



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