64f.18. Crataegus Linnaeus (sect. Coccineae) ser. Triflorae (Beadle) Rehder, Man. Cult. Trees ed. 2. 364. 1940.
Crataegus [unranked] Triflorae Beadle in J. K. Small, Fl. S.E. U.S., 533, 537. 1903; Crataegus sect. Triflorae (Beadle) C. K. Schneider
Shrubs, 20–50 dm, ˂trunks fasciculate˃, multi-stemmed. Stems: trunk bark younger grayish, smooth, sometimes exfoliating in irregular papery patches, mature rough, gray-brown; ˂branches spreading; twigs ± straight˃, new growth pubescent, 1-year old mid brown, older gray; thorns on twigs sparse to moderately frequent, ± straight, 2-years old dark gray or blackish, ± thin, 2–4 cm. Leaves: petiole length 33% blade, ˂winged distally˃, densely pubescent, stipitate-glandular; blade ˂mid to dark green˃, broadly ovate to broadly elliptic or nearly suborbiculate, 3–8(–10) cm, ± chartaceous, base broadly cuneate to rounded or truncate, lobes 0 or 1–3(or 4) per side, sinuses shallow, lobe apex subacute to acute, margins regularly, sharply glandular-serrate, ˂proximally usually stipitate-glandular˃, venation craspedodromous, veins 5–7 per side, apex acute to subacute, abaxial surface mainly hairy on veins, adaxial hairy until maturity. Inflorescences 2–6(–12)-flowered, reduced or larger convex panicles, ˂usually borne on leafy short shoots of season lateral to extension shoots, sometimes also on woody short shoots˃; branches densely tomentose (intermixed with stipitate glands); bracteoles caducous to semipersistent, ˂ligulate˃, linear, ˂large˃, membranous to herbaceous, margins stipitate-glandular. Flowers 25–30 mm diam.; hypanthium densely tomentose; sepals ˂foliaceous˃, triangular, wide, 2/3–3/4 length of petals, ˂herbaceous˃, margins glandular-pectinate, ˂abaxially pubescent˃; ˂petals broadly elliptic in C. austromontana˃; stamens 10 or 30–45(–47), anthers cream; styles 3–5. Pomes ˂1–few per infructescence˃, red to ruddy, suborbicular to obovoid, 12–15 mm diam., hairy; flesh mealy to ± hard; sepals ˂persistent˃, patent-reflexed, ˂long, non-accrescent˃; pyrenes 3–5.
Species 2 (2 in the flora): se United States.
Series Triflorae comprises one relatively common (Crataegus triflora) and one rare (C. austromontana) species, occurring from Louisiana to Georgia in the piedmont and north into Tennessee, with an outlier in Arkansas. The species are found in brush, including prairie margins and open woodlands; they are also able to tolerate considerable shade.
Species in ser. Triflorae are characterized by few- and large-flowered inflorescences, often borne on lateral leafy short shoots of the season, as well as by very glandular petioles, leaf margins, pedicels, and sepal margins, which are also usually very hairy. Also characteristic are the multiple stems lacking main trunk dominance. The most similar series is ser. Bracteatae. The 30–45 stamens of Crataegus triflora are unique in the genus.