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Pakistan | Family List | Brassicaceae

Arabis Linn., Sp.P1. 644. 1753. Gen. Pl. ed. 5:298. 1754; Schulz in Engl. & Prantl, l.c. 542; Busch in Kom., l.c. 172; Cullen in Davis, l.c. 422; Hedge in Rech. f., l.c. 201; Jafri in Notes Roy. Bot. Gard. Edin. 22:98-101.1956.

Arabis tibetica
Illustration

Credit: Shaukat & Azmat

Annual, biennial or perennial herbs, usually ± hairy with simple, forked or stellately branched hairs, sometimes glabrous above. Rosette leaves usually stalked and hairy; cauline leaves 0-many, usually sessile, amplexicaul; all leaves usually dentate. Racemes often lax in fruit, generally ebracteate. Flowers mediocre or large, white, pinkish or violaceous, often turning dull-yellowish when dried; pedicels often elongating in fruit, ascending rarely spreading. Sepals slightly to distinctly saccate at base, erect or suberect. Petals about twice as long as the sepals, obovate-oblong, shortly clawed. Stamens 6, filaments not appendaged; anthers oblong-linear. Lateral nectar glands usually annular, incomplete; middle often minute, usually conical, not joining the laterals. Ovary linear, many ovuled; stigma depressed, usually on a distinct style. Siliquae linear-oblong, usually strongly compressed with a distinct mid-vein on the valves, and glabrous (rarely pubescent), bilocular, dehiscent, many seeded; seeds ovate, compressed, sometimes narrowly margined (winged); septum membranous, not veined; radicle usually accumbent.

About 100 species, mostly throughout the North Temperate zone and S. America; only 9 species recorded for our area.

A difficult genus due to polymorphic nature of its several species and over-lapping of characters in some of our species is not uncommon. Furthermore, it also tends to overlap the characters of some of the species of the genus Aradidopsis of the tribe Sisymbrieae, where the radicle is incumbent and flowers smaller with seeds normally mucilaginous when wet. Arabis tenuisiliqua Rech. f. & Koeie from Afghanistan, should better be transferred to Arabidopsis and called Arabidopsis tenuisiliqua (Rech. f. & Koeie) Jafri, comb. nov. (Arabis tenuisiliqua Rech. f. & Koeie in Oester. Akad. Wiss. 7:5. 1954). This species has been described in fruits only which resemble very closely to siliquae in some species of Arabidopsis, and the radicle is also incumbent but seeds not mucilaginous when wet. This is a similar case as that of Arabidopsis eseptata Hedge or Arabis taraxacifolia T. And., which has now been transferred to Arabidopsis.

difference of radicle forms in the two genera seem to be the only separating factor to keep them under 2 different tribes, which may be restudied thoroughly, to decide the transfer of Arabidopsis to the tribe Arabideae. However, genera like Phaeonychiurn, do have incumbent radicles in this tribe also, and Arabidopsis eseptata Hedge has seeds non mucilaginous when wet.


1 Cauline leaves absent (rarely 1-2, sparsely hairy with simple or furcated hairs)   Arabis saxicola
+ Cauline leaves usually many (rarely 1-2 in A tibetica but densely hairy with branched or stellate hairs)   (2)
       
2 (1) Siliquae obtuse, densely pubescent; style absent or inconspicuous   Arabis fruticulosa
+ Siliquae ± acute, glabrous (rarely sparsely pubescent); Style ± distinct   (3)
       
3 (2) Cauline leaves cuneate or narrowed at the base, often subsessile   (4)
+ Cauline leaves with ± broad bases, sessile, amplexicaul or semi-amplexicaul   (5)
       
4 (3) Plants 5-15 (-20) cm tall, much branched from the base perennating   Arabis tibetica
+ Plants 20-50 cm tall, not much branched, annual or biennial   Arabis tenuirostris
       
5 (3) Annual; pedicels usually short and somewhat thickened 2-5 mm long; siliquae glabrous or sparsely pubescent with Short stellate hairs   Arabis nova
+ Perennial; pedicels usually long, (6-) 8-25 mm, not thick-ened; siliquae glabrous   (6)
       
6 (5) Plants subglabrous or sparsely hairy; petals large, c. 14 mm long (in ± diverging pairs); (upper leaves not so broad at base, oblong-elliptic or linear, distant)   Arabis bijuga
+ Plants usually more hairy, often hispid; petals 5-10 mm long; (not in diverging pairs); (upper leaves ovate to elliptic oblong)   (7)
       
7 (6) Cauline leaves few (1-) 2-4, usually narrowly oblong, some what narrowed at base, semiamplexicaul; radical leaves stellately hairy   Arabis pangiensis
+ Cauline leaves usually many (more than 5) ± broad at the base, amplexicaul (usually apparently auricled at base); radical leaves usually hairy with simple or branched hairs   (8)
       
8 (7) Siliquae ± erect or suberect with inconspicuous style (c. 0.5 mm long) and usually on c.10 mm long pedicels; rosette leaves usually small, 2-4 cm long, 0.5-1.5 cm broad, often hispid   5 Arabis pterosperma
+ Siliquae ± spreading with conspicuous style (1-1.5 mm long) and usually on c.15 mm long pedicels; rosette leaves usually large, (5-) 6-15 cm long, 2-3 cm broad, ± hairy   Arabis amplexicaulis

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