Vascular Plants of Williamson County

Youngia japonica [Asteraceae]
japanese hawkweed, oriental false hawksbeard

Youngia japonica (L.) DC., japanese hawkweed, oriental false hawksbeard.  Annual, taprooted, flat–rosetted, 1–stemmed at base, scapose, ascending, in range to 35 cm tall; shoots with only basal leaves, foliage with thin blades, in range having soft hairs with beadlike cells (moniliform); latex milky.


Stem in range basal concealed by leaves.


Leaves helically alternate, coarsely toothed and pinnately lobed, in range 65—160 mm long, petiolate, without stipules; petiole ± cylindric flattened on upper side, to 50 mm long, indistinct from blade, sheathing and whitish at base to green approaching blade, with a pair of pinkish stripes (ridges) along upper side, pubescent especially close to stem; blade obovate to elliptic in outline with a dominant, large terminal lobe, < petiole, with scattered hairs, terminal lobe 25—65 × 20—45 mm, dentate with or without shorter basal lobes, obtuse with short point at tip, pinnately veined with principal veins sunken on upper surface and raised on lower surface, below terminal lobe with diminutive, short lobes and teeth along midrib reduced toward petiole.


Inflorescence heads, in cymelike arrays on ascending axes, having 1—several widely spaced clusters of heads, head ligulate, ca. 9 mm across, in range < 25–flowered, bracteate, essentially glabrous; axis cylindric, ca. 2 mm diameter, reddish at base to green above, with some hairs near base; bract subtending branchlet and peduncle linear–triangular, to 3.5 mm long decreasing upward, colorless and reddish at tip; branchlet angled, coarsely short–hairy; peduncle 3—4–sided or cylindric, < 12 × 1 mm, green to reddish, glabrous or sparsely short–hairy; bracts subtending involucre (calyculus) (3—)5, ovate, 1—1.6 mm long, green with colorless or reddish wide margins and tip, with pulvinuslike bump at base, glabrous; involucre bell–shaped, of 8 phyllaries in 2 series, phyllaries ascending, ca. 5 mm long, ± keeled to midpoint, green with colorless margins continuous to tip, short–ciliate on margins at tip, green surface glabrous; receptacle slightly convex and with slightly sunken ovaries, lacking bractlets (paleae) and hairs.


Flower bisexual, bilateral, ca. 1.3 mm wide; calyx (pappus) of ca. 40 capillary bristles in 2 series, bristles straight, 2.5—2.8 mm long, white, fused at base; corolla 5–toothed, exserted 1—2 mm beyond involucre; tube cylindric, < 1.5 × 0.3—0.35 mm, white at base to yellowish approaching limb, with scattered short hairs above midpoint; limb strap–shaped, 3.7—4 × 1.2—1.3 mm, light yellow with reddish teeth, teeth acute, ± 0.3 mm long; stamens 5, fused to top of corolla tube; filaments slender, 1 mm long, yellowish at least to midpoint; anthers fused as cylinder surrounding style, basifixed, dithecal, 1 mm long + colorless, linear tails ca. 0.35 mm long, anther sacs purplish red, longitudinally dehiscent; pistil 1; ovary inferior, obovoid compressed side–to–side, 0.7 × 0.25—0.3 mm, greenish white, glabrous, 1–chambered with 1 ovule; style 4 × 0.25 mm, yellowish base–to–tip, 2–branched, short–hairy inside anthers, the branches spreading to recurved nearly 360°, ca. 0.5 mm long, papillate on upper side.


Fruits cypselae (achenes), with persistent pappus of ca. 40 capillary bristles fused at base, 5—6 mm across, silky white; cypsela fusiform, in range ca. 1.5 × 0.5 mm, dull brown, with hollow base, conspicuously ribbed, the ribs ca. 15 with upward–pointed barbs (antrorse).

A. C. Gibson