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FOC | Family List | FOC Vol. 8 | Brassicaceae

48. Arabis Linnaeus, Sp. Pl. 2: 664. 1753.

南芥属 nan jie shu

Parryodes Jafri.

Herbs annual, biennial, or perennial, rarely subshrubs or shrubs. Trichomes stellate, dendritic, or stalked forked, sometimes mixed with fewer simple ones, rarely primarily simple. Stems simple or branched apically. Basal leaves petiolate, rosulate, simple, often entire, sometimes dentate, rarely lyrate-pinnatifid. Cauline leaves sessile and auriculate, sagittate, or amplexicaul, very rarely petiolate, entire or dentate. Racemes ebracteate or rarely bracteate throughout or only basally, sometimes in panicles, elongated in fruit. Fruiting pedicels erect, ascending, divaricate, or reflexed. Sepals ovate or oblong, base of lateral pair saccate or not, margin membranous. Petals white, pink, or purple; blade spatulate, oblong, or oblanceolate, rarely obovate, apex obtuse or emarginate; claw shorter than sepals. Stamens 6, tetradynamous; filaments usually not dilated at base; anthers ovate, oblong, or linear, obtuse at apex. Nectar glands confluent, subtending bases of all stamens; median glands sometimes toothlike and free, rarely absent; lateral glands semiannular or annular. Ovules 12-110 per ovary. Fruit dehiscent siliques, linear, latiseptate, sessile or rarely shortly stipitate; valves papery, with an obscure or prominent midvein, smooth or torulose; replum rounded; septum complete, membranous, translucent, veinless; style obsolete or distinct; stigma capitate, entire or slightly 2-lobed. Seeds uniseriate or biseriate, winged or margined, oblong or orbicular, flattened; seed coat smooth or minutely reticulate, not mucilaginous when wetted; cotyledons accumbent.

About 70 species: temperate Asia, Europe, North America; 14 species (one endemic) in China.

The limits of Arabis are highly artificial, and the genus is defined primarily on the basis of having branched trichomes, flattened, linear fruit, and accumbent cotyledons. However, this combination of characters has evolved independently several times in the Brassicaceae. A critical study of the genus on worldwide basis is much needed.

1 Racemes bracteate throughout   10 A. axilliflora
+ Racemes ebracteate, rarely lowermost 1-3 flowers bracteate.   (2)
2 (1) Annuals; fruiting pedicel thickened, at least half as wide as fruit; rachis flexuous   14 A. auriculata
+ Biennials or perennials; fruiting pedicels much narrower than fruit; rachis not flexuous.   (3)
3 (2) Shrubs or subshrubs; style absent or obsolete; fruit densely pubescent   12 A. fruticulosa
+ Herbs; style distinct; fruit glabrous or if pubescent (A. flagellosa) then leaves dentate.   (4)
4 (3) Scapose perennials with caudices covered with petioles of previous years; trichomes almost exclusively simple, restricted to leaf margins and sepals abaxially; stems leafless or with 1-3 leafy bracts   11 A. alaschanica
+ Non-scapose biennials or perennials often without petioles of previous years; trichomes a mixture of various kinds, very rarely restricted to leaf margins; stems leafy.   (5)
5 (4) Cauline leaves petiolate or cuneate to petiolelike base; fruit valves with an obscure midvein.   (6)
+ Cauline leaves sessile, auriculate, sagittate, or amplexicaul, rarely rounded at base; fruit valves often with a prominent midvein.   (7)
6 (5) Biennials; petals 3-5 mm; fruit apex acuminate; Xizang [Kashmir, Afghanistan, Pakistan, Tajikistan]   13 A. tibetica
+ Stoloniferous perennials; petals 7-10 mm; fruit apex acute; Anhui, Jiangsu, Zhejiang [Japan]   9 A. flagellosa
7 (5) Fruit and often fruiting pedicels erect, appressed to rachis.   (8)
+ Fruit and fruiting pedicels divaricate or reflexed, fruit sometimes erect on divaricate or ascending pedicels never appressed to rachis.   (10)
8 (7) Petals (3.5-)4-5 mm; fruit 0.8-1.2 mm wide   8 A. hirsuta
+ Petals 6-10 mm; fruit 1.5-2 mm wide.   (9)
9 (8) Petals white, 3-4 mm wide, apex shallowly emarginate; sepals 4-5 mm, lateral pair saccate; middle cauline leaves pilose with primarily branched trichomes; seeds narrowly winged distally   6 A. stelleri
+ Petals purple, pink, or rarely white, 2-3 mm wide, apex rounded; sepals 2.5-3.5 mm, lateral pair not saccate; middle cauline leaves hirsute with predominantly simple trichomes; seeds broadly winged all around   7 A. pterosperma
10 (7) Petals 3-6(-6.5) mm; lateral sepals not saccate; style in fruit 0.2-0.8 mm.   (11)
+ Petals 7-15 mm; lateral sepals saccate; style in fruit 1-2.5 mm.   (12)
11 (10) Basal rosette absent at anthesis and fruiting; leaves with coarse subsetose trichomes mixed with sessile, much smaller stellate ones; fruit reflexed or divaricate, 1.5-2 mm wide   4 A. pendula
+ Basal rosette often present through fruiting; leaves with stalked, forked or 3- or 4-rayed stellate trichomes mixed with simple nonsetose ones; fruit ascending or erect, rarely reflexed or spreading, 1-1.5 mm wide   5 A. paniculata
12 (10) Plants hirsute or hispid with primarily simple, subsetose trichomes   1 A. amplexicaulis
+ Plants tomentose or pilose with almost exclusively branched trichomes, sometimes glabrescent.   (13)
13 (12) Leaves obtuse or auriculate at base; filaments 5-8 mm; petals 9-14 mm, obtuse at apex; 2-forked trichomes distinctly stalked   2 A. bijuga
+ Leaves cordate or amplexicaul at base; filaments 4-5 mm; petals 7-10 mm, truncate-emarginate at apex; 2-forked trichomes often submalpighiaceous   3 A. serrata

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