danielatha's Journal

Revised from Atha, D. E., M. H. Nee & R. F. C. Naczi. 2010. Persicaria extremiorientalis (Polygonaceae) is established in the flora of the eastern United States of America. The Journal of the Torrey Botanical Society 137: 333–338. https://doi.org/10.3159/10-RA-033.1

Figure 1. Whole plant (top left): www.inaturalist.org/observations/7877986. Stem internode (top right): www.inaturalist.org/observations/183785156. Flowers and achenes (bottom left): www.inaturalist.org/observations/185228896. Leaf marginal hairs (bottom right): www.inaturalist.org/observations/186240490.

Field work and herbarium study on the genus Persicaria (L.) Mill. revealed a robust, weedy, terrestrial herb reaching 2 m or more in height with pilose stems and purplish, nodding inflorescences that did not fit any species then described in floras or monographs of American Polygonaceae (Meisner 1856, Small 1895, Fernald 1950, Dalci 1974, Gleason and Cronquist 1991, Hinds and Freeman 2005). The species is not described in the Flora of China (Li et al. 2003), but in that work keys out to Polygonum persicaria L. (Persicaria maculosa S. F. Gray). The plant does however, answer to Persicaria extremiorientalis (Vorosch.) Tzvelev as described in the Flora of the Russian Far East (Tzvelev 1989) and Persicaria maculosa subsp. hirticaulis (Danser) S. Ekman and T. Knutsson var. pubescens (Makino) Yonek., pro parte, as described in the Flora of Japan (Yonekura 2006).

The species was first collected in North America by Joseph Vincent Monachino and J. Boxer in Queens and Brooklyn, New York, in 1961 (30 July, Monachino 636; 13 August, Monachino 641; 16 August, Boxer s.n). It was next collected in Stamford, Connecticut on 17 August 1962 by Frank Seymour and B. Wakeman (20311); in Bronx, New York on 26 October 1974 by T. J. Delendick (Delendick s.n.) and then more frequently in the 1980’s, 1990’s and throughout the 2000’s by numerous collectors (principally by staff of the Brooklyn Botanic Garden and The New York Botanical Garden). Most of the specimens were misidentified as Polygonum lapathifolium L. (Persicaria lapathifolia (L.) Delarbre) and/or Polygonum persicaria (Persicaria maculosa), and remained so until the present study.

Many of the approximately 100 species of Persicaria section Persicaria are polyploids, and hybridization is suggested in several instances (Greene 1904, Stanford 1925, Fassett 1949, Timson 1964, Mitchell and Dean 1978, McDonald 1980, Consaul et al. 1991, Kim and Donoghue 2008b). Recent molecular studies document extensive incongruence between sequences in the chloroplast and nuclear genomes, and allopolyploid speciation is suggested for several species (Kim et al. 2008, Kim and Donoghue 2008a, Kim and Donoghue 2008b). Not surprisingly then, there is only weak support for a classification system within Persicaria section Persicaria, and few have been attempted since Meisner’s global monograph of Polygonum s.l. (Meisner 1856).

Uncertain boundaries of individual species and lack of resolution within section Persicaria, combined with the fact that Persicaria extremiorientalis shares character states almost equally with Persicaria lapathifolia and Persicaria maculosa, but also exhibits some not shared by either, argue strongly against recognition as a subspecies and/or variety of either species (as is done in the Flora of Japan).

The binomial Persicaria extremiorientalis is the earliest name unequivocally applicable at the species level for this taxon.

Type specimens and the numerous collections from throughout the range in Asia and eastern North America superficially resemble Persicaria lapathifolia and Persicaria maculosa, but consistently differ from both in several significant characters. The three most consistent character states that distinguish this species from all other Persicaria are: 1, basal stem internodes with appressed hairs; 2, leaf margin setae 0.5–1.1 mm long; and 3, achenes compressed laterally, brown, lustrous and basally tumescent (swollen).

Key to distinguish Persicaria extremiorientalis from the allied Persicaria lapathifolia and Persicaria maculosa

A. Stem internodes glabrous; ocrea outer surfaces glabrous, the apex glabrous; leaf blade margins glabrous or setose with setae , 0.2 mm long, the abaxial surface lanate, arachnoid, or glabrous, glandular-punctate when glabrous; bracts glabrous, the apex caudate or long-acuminate; fruiting tepal vein apices bifurcate and both branches strongly and consistently recurved...........Persicaria lapathifolia.

A. Stem internodes pubescent or glabrous; ocrea outer surfaces strigose, the apex ciliate or setose; leaf blade margins setose, the setae 0.2–1.1 mm long, the abaxial surface strigose, eglandular; bracts sparsely strigose, the apex truncate to obtuse; fruiting tepal vein apices bifurcate or unbranched, if branched, only one branch weakly recurved (never both)...........B.

B. Basal stem internodes glabrous; leaf margin setae 0.2–0.5 mm long; peduncles rarely stipitate-glandular; racemes 1–4 cm long, erect; fruiting tepal veins prominently raised when dry; achenes lenticular or trigonous, basally widest but not tumescent..........Persicaria maculosa.

B. Basal stem internodes with appressed hairs; leaf margin setae 0.5–1.1 mm long; peduncles usually short stipitate glandular; racemes usually 3–8 cm long, usually nodding; fruiting tepal veins not prominently raised when dry; achenes lenticular (rarely trigonous), basally tumescent..........Persicaria extremiorientalis.

Herbs, annual, (0.1–)0.4–2.3 m tall, from slender to stout taproot; stems up to 2 cm diam at the base, proximally unbranched or few-branched, reddish-brown to purple, the proximal and medial stems pilose, rarely glabrate or appressed-setose, the trichomes basally slightly enlarged, distally slender, pale and slightly undulate, 1–5 mm long; ocrea membranous, pale greenish-yellow, somewhat translucent, 12–24 ribbed, the dorsal surface strigose, especially along the ribs, rarely glabrous, 1.3–2.5 cm long, the apices (margins) truncate, setose, the setae 1–5 mm long. Leaves largest proximally, diminishing distally; petioles 1–3 cm long, appressed-setose; blades narrowly ovate, (6–)10–28 3 1–7 cm, the adaxial surface dark green, usually with obscure, but large, central, purple chevron, very regularly and sparsely strigose, the abaxial surface lighter green, evidently eglandular, very regularly (but moderately sparse), golden-strigose, minutely papillose, the base cuneate, the margins entire, appressed-setose, the trichomes arched acroscopically, 0.5–1.1 mm long, the apex long-acuminate; vena- tion pinnate, the abaxial midvein appressed- setose, the trichomes stout, deltoid, the sec- ondary veins arcuate, 12–35 pairs, usually setose. Inflorescences axillary and terminal, leafy; peduncles stipitate-glandular (sometimes the glands very minute or nearly wanting), sometimes also shortly appressed-setose; ra- cemes (1.5–)3–8 cm long, 5–8 mm diam, densely flowered, usually purplish, rarely greenish-white, basally uninterrupted, usually nodding at maturity; bracts ascending, ovate, the dorsal surface sparsely strigose, green- striate, the apices obtuse to acute, setose, the setae ca. 0.2 mm long. Flowers ca. 6 per fascicle-like partial inflorescence, 2 mm long, white at anthesis, soon accrescent and becoming pinkish-purple; pedicels ca. 1.5 mm long, slightly exserted from the bracts; hypanthium 1/5–1/3 length of flower; tepals (4)5, ca. 1 mm long (at anthesis), elliptic, the apices obtuse or rounded, the outer 2 slightly cucullate and slightly exceeding inner, the inner 6 plane; veins trifid-branched above the base, erect, not raised when dry, distally straight and unbranched or rarely and inconsistently bifurcate, one branch then divergent, but not recurved; stamens 5, inserted at the apex of the hypanthium and alternating with the tepals, ca. 0.8 mm long, included; floral glands apparently absent; ovary glabrous, lenticular; styles 2, united about 1/2 the length, distally divergent and slightly recurved, caducous in fruit. Achenes lenticular (rarely trigonous), (1.8–)2.0–2.3 x 1.5–1.9 mm, the faces plane to concave, both faces basally tumescent, the base rounded, the apex obtuse, short-apiculate; pericarp mahogany-brown, lustrous, minutely sculptured.

Discussion

Very few species of Persicaria have one or two characters that consistently distinguish one species from another; usually a combination of three or more characters is required to distinguish a species. For example, early- blooming or depauperate specimens of Persicaria extremiorientalis have short, erect racemes, like those of Persicaria maculosa. However, the stems will be hirsute (glabrous in Persicaria maculosa) and the leaf blade margins will have setae 0.5 mm long (<0.5 mm in Persicaria maculosa).

Further complicating identification is the fact that several species exhibit extreme variation in gross morphology. The cosmopolitan Persicaria lapathifolia may be ten centimeters tall and have very narrow, eglandular, lanate leaves, or it might be 2 m tall and have wide, glandular, and glabrous leaves. However, both variants will have tepal veins that are distally branched and recurved. There is a seemingly infinite series of intermediates (in habit and leaf characters) spanning the morphological range from one variant to the other (often within a population), but all have glabrous ocrea and inflorescences and have recurved tepal veins.

Persicaria extremiorientalis exhibits a similar broad range of variation in its habit. Early in the season or in marginal habitats, plants are very slender and flower when only 10–20 cm tall. Later in the season and under ideal conditions, they are robust from a stout taproot and flower when two or more meters tall. In habit, Persicaria extremiorientalis strongly resembles Persicaria lapathifolia. In Persicaria extremiorientalis, the central leaf blade adaxial surface in age is pigmented dark purple (unpigmented in Persicaria lapathifolia). It shares the strigose ocrea and bracts with Persicaria maculosa (glabrous in Persicaria lapathifolia). It shares with Persicaria lapathifolia the tendency to have stipitate-glandular peduncles and nodding racemes (eglandular peduncles and erect racemes in Persicaria maculosa). The racemes are usually strongly pigmented pink to purple as in Persicaria maculosa (racemes usually yellow-green or weakly pink tinged in Persicaria lapathifolia). Both Persicaria lapathifolia and Persicaria maculosa have prominent tepal veins, but in Persicaria lapathifolia, they are very prominently raised (when mature and dry), and the apices are always bifurcate with both branches strongly recurved (sometimes called ‘‘anchor veins’’). In Persicaria maculosa the tepal veins are usually prominent, but the apices rarely branch and are never recurved. In Persicaria extremiorientalis the tepal veins may or may not be prominent and sometimes bifurcate, but then only one branch is divergent.

Plants as conspicuous and weedy as the present species would have been noted by prior monographers and collectors, yet no plants like those described here were reported or collected in North America prior to 1961. We therefore hypothesize that the species was introduced sometime shortly before this date. As demonstrated here, the species appears to blend character states from Persicaria lapathifolia and Persicaria maculosa. We hypothesize that Persicaria extremiorientalis is a hybrid of relatively recent origin in eastern Asia, probably involving Persicaria maculosa and Persicaria lapathifolia. Both putative parents are abundant, wide- spread weeds and often co-occur in urban, disturbed, or early successional areas–the same habitats in which American and Asian Persicaria extremiorientalis are found.

Of the numerous populations sampled, none are from undisturbed, climax communities, such as forests, wetlands or grasslands. One of the New York Botanical Garden populations (Atha 6839) consisted of 5 individuals of various sizes in 2008, but throughout the following year and early summer of 2010, none were found at this site.

The Asian congener, Persicaria caespitosa Blume var. longiseta (Bruijn) A. N. Steward was first discovered near Philadelphia in 1910 and by 1940 had spread north to Massachusetts and south to Maryland. By 1991 it was found in every state east of the Mississippi River as well as Nebraska, Iowa, Missouri, Arkansas and Louisiana (Patterson, 2000). These plants invade mesic forests, wetlands, lawns, gardens and waste places throughout the eastern United States, and persist in the same place from year to year, displacing native species. Although Persicaria extremiorientalis appears to be ephemeral from year to year (unlike the persistent Persicaria caespitosa var. longiseta), its spread westward may be expected.

[Addendum October 2023]
The species has now been documented from Maine to South Carolina and west to Akron, Ohio and is probably more widespread than that.

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