Juncus tenuis Willd.

  • Authority

    Balslev, Henrik. 1996. Juncaceae. Fl. Neotrop. Monogr. 68: 1-167. (Published by NYBG Press)

  • Family


  • Scientific Name

    Juncus tenuis Willd.

  • Type

    Type. U.S.A.  America boreali, collector unknown (lectotype, B-W 6888! sheet 1, here selected; isotypes, B-W 6888! sheets 2, 3, and 4, HBG!; photo, AAU!; fragment, NY!).

  • Description

    Species Description - Perennial, cespitose herbs, 15-70 cm tall. Rhizome densely branching, 1.5-2 mm diam. Culms erect, terete, smooth or longitudinally ridged, 0.8-1.5 mm diam. Cataphylls 0-3 per culm, inconspicuous, to 5 cm long, margin scariose, rudimentary blade acicular, to 15 mm long. Foliar leaves all basal, erect, 1/3 of to equalling the length of culm; sheaths 1.5-9 cm long, with scariose margins terminating in 2 scariose or cartilaginous auricles; blade linear, flat or terete and canaliculate in x.s., 0.5-1.5 mm wide. Inflorescence terminal on the culm, occupying less than ¼ of the total plant height, compound-cymose, consisting of several unilateral cymes (drepania). Lower inflorescence bract resembling basal leaves, herbaceous, 2-20 cm long, distal ones progressively shorter, ultimate ones scariose to 5 mm long. Bracteoles 2 to each flower, 1.5-2 mm long. Tepals unequal, lanceolate, acute to acuminate, first green with distinct scariose margin, turning brown to stramineous, outer tepals 3.5-5 mm long, concave, inner tepals 3-4.5 mm long, flat. Stamens 6, 1.3-1.8 mm long; anthers linear to oblong, 0.40.8 mm long. Capsule ellipsoid, acute to obtuse, apiculate, 2.5-3.5 x 2-2.5 mm, light brown at maturity, 3-septate. Seeds ellipsoid, apiculate, often curved, 0.4-0.6 x 0.2-0.3 mm, smooth to slightly rugose, yellow-brown.

  • Discussion

    Distribution and Ecology: Juncus tenuis is a widespread and common species in North America. It was introduced in the 19th century from North America to western Europe where it is now widespread and still extending its range. Scattered introductions are found in Japan, the Azores, and New Zealand. In the neotropical region this species is found throughout the highlands. Juncus tenuis belongs to a North American species complex in need of revision. Wiegand (1900) clarified some problems, but his study is now outdated. The morphological variation of the neotropical populations suggests that they are the result of several introductions from temperate North America. A satisfactory solution of the taxonomy of J. tenuis in the neotropical region depends on a revision of the entire complex in North America. I have here, provisionally, divided the species into three varieties. These varieties cannot be distinguished by any single character mentioned in the key, but by using more than one character the large majority of specimens key out.