Thlaspi montanum var. siskiyouense P.K.Holmgren
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Authority
Holmgren, Patricia K. 1971. A biosystematic study of North America Thlaspi montanum and its allies. Mem. New York Bot. Gard. 21: 1-106.
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Family
Brassicaceae
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Scientific Name
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Description
Latin Diagnosis - A caeteris T. montani varietatibus his notulis absimilis: foliorum basalium petiolus pro rata elongatus (13-)15-34(-50) mm longus laminae suae (5-)6-13(-15) mm longae (1.7-)2-3.6(-4.1)-ies longior; caulis infra racemum fructiferum (2.5-)4-12(-17) cm longus; siliculae latiusculae (3-)3.5-5.5(-6) mm latae, apice truncatae vel profunde emarginatae, plerumque alatae; pedicelli horizontales vel horizontali- descendentes; foha basalia saepe ante siliculas maturatas emortua.
Species Description - Glabrous, occasionally glaucous, short-lived perennial (5.5-)7-16(-24) (averaging 12) cm tall at maturity, with a simple to freely branched caudex; stems 1-9(-14), simple, slender, about (0.6-)0.8-1.4(-2) mm thick at tip of upper cauline leaf, (2.5-)4-12(-17) (averaging 12) cm long below the infructescence, greenish or purplish, becoming straw-colored as fruit ripens; basal leaves numerous, frequently drying and withering before ripening of fruit, (16-)22-44(-52) (averaging 33) mm long, 4-8(-9) (averaging 5.5) mm wide, the blade (5-)6-13(-15) mm long with a (13-)15-34(-50) mm (comparatively very long) petiole (1.7-)2-3.6(-4.1) times as long as the blade; cauline leaves (2-)3-6, greenish or purplish, with a very narrow, entire (seldom denticulate), hyahne margin, (5-)7-11(-15) mm long, becoming withered in fruit, sessile and auriculate-clasping; petals white, spatulate, 3.8-6 mm long, 1.2-2.2 (-2.9) mm wide; sepals greenish but often purplish especially toward the tip, with a narrow hyahne border, mostly rounded to obtuse at the apex, (1.8-)1.9-2.8 mm long; longer stamens 1.7-3.0 mm long, anthers yellow; infructescence (1.5-)2-8(-11.5) (averaging 4.8) cm long, (2-)2.5-3.3(-3.5) cm wide, from loosely to fairly compact, the pedicels (4-)5-13(-20) in the lower 2 cm of infructescence, mostly horizontal to horizontal-descending, the lower ones (3.5-)5-9(-9.5) mm long, becoming shorter upwards; silicles mostly horizontal, obovate to obdeltoid, from truncate to strongly emarginate at the apex, mostly strongly winged, greenish to purplish, (4-)4.8-7(-8) (averaging 6) mm long, (3-)3.5-5.5(-6) (averaging 4.5) mm wide, the length (1-)1.2-1.6(-1.8) times the width; seeds 2-4 per silicle, 1.6-2.0 mm long, dark brown, lightly striate, some with a prominent raphe; style (0.8-)1.0-1.9(-2) mm long; stigma (0.15-)0.2-0.3 mm thick. Flowering time: April-June. Chromosome number: n = 7.
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Discussion
Type. Oregon, Kerby Flat at base of Eight Dollar Mountain above Illinois River, 2 miles west of Selma, 18 May 1942, L. Constance & R. Rollins 2972 (holotype, WTU!; isotypes, GH!, MO!, NY!, RM!, UC!, US!, UTC!).
This variety is recognized by a combination of the following morphological features: a) basal leaves with petioles very long in relation to blade length; b) silicles relatively wide, with a truncate to strongly emarginate apex; c) pedicels horizontal to horizontal-descending; and d) coloration frequently purplish. T w o scatter diagrams (Figs. 17, 18) depict a portion of the combination of characters separating var siskiyouense from the other varieties.
Aside from the morphological distinctiveness, var siskiyouense has an elevational range (1200-1600 feet) below that of all our other taxa except for a few records of occurrence of var montanum in northern California at 400-1000 feet elevation (see discussion under var montanum). Geographically, var montanum closely approaches var siskiyouense, perhaps to within five to ten miles at Elk Valley in northern Del Norte County, California (J. P. Tracy 19099, MSC, UC, WTU). Ecologically, however, this population would be isolated from var siskiyouense by its later flowering period, as well as by elevation, occurring as it does at 4400 feet. Herbarium specimens indicate that var siskiyouense may be sympatric with var montanum near Waldo, Oregon.
Of the Thlaspi collections which I have examined from extreme southwestern Oregon (Josephine County), all but three are readily referable to var siskiyouense. Of the three, two are from near Waldo \T. Howell (1073 marked on one sheet), 24 Apr 1887, MO, NY, UC, W T U , and J. W . Thompson 2235, WTU J. The Howell collection is a mixture of var siskiyouense and var montanum. The Thompson collection is intermediate, most closely matching var montanum, but with the leaves of var siskiyouense. Another Howell collection, 5 Jun 1884 (DAO, GH, NY-2, S) from near Waldo, is clearly assignable to var siskiyouense, so it would appear that the two taxa may be sympatric and probably intergradient in that area. The other intermediate collection is from the northern part of the county on Slate Creek, Piper 6173 (GH, US, WTU). The three sheets seen contain eighteen plants or portions thereof, of which the fruits (except those on three plants) match var montanum, whereas the majority of the basal leaves more closely resemble those of var siskiyouense.
Payson (1926) cited only two specimens from southwestern Oregon (both at MO), referring them to T. glaucum var hesperium. One of these is the Howell collection (Howell 1073) from near Waldo mentioned above. The other one is a Joseph Howell collection from the Siskiyou Mountains, which I have referred to var montanum.
The petioles of the basal leaves of var siskiyouense remain long and slender in greenhouse cultivation (Fig. 14). The leaves for these photographs were taken from three sources: a) the original collections (Kern 743) in 1965; b) the original collection presently living in the greenhouse (Kern 743); and c) plants raised from seed (Kern 743) in 1966.
Fruits and seeds of var siskiyouense always required one to two weeks longer to ripen than those of any other population of Thlaspi tested in the greenhouse. Variety siskiyouense (n = 7) will cross, in varying degrees, with diploid var montanum, but does not produce any good seeds when crossed with tetraploids. It will cross in only one direction to var idahoense and crosses in very low percentage (14%) with T. alpestre. Figure 48 depicts crossability of this variety as well as stainable pollen percentage of the F1's.
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Distribution
Distribution (Fig. 65). Growing mostly on serpentine, commonly on moist, open, rocky slopes in Josephine Co., Oregon, at 1200-1600(2000?) feet elevation. OREGON. Josephine County: Highway 199, 0.7 mi S of Rough-and-Ready Creek, T40S, R8W, Sect. 18, 18 Mar 1967, K. L. Chambers & G. York 2481 (OSC), Kerby Flat at base of Eight Dollar Mt., above Illinois River, 2 mi W of Selma, 1200 ft, 18 May 1942, L. Constance & R. C. Rollins 2972 (GH, MO, NY, RM, UC, US, UTC, WTU), Deer Creek, T38S, R8W, Sect. 9
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