Cassia artemisioides DC.
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Authority
Isley, Duane. 1975. Leguminosae of the United States: II. Subfamily Caesalpinioideae. Mem. New York Bot. Gard. 25 (2): 1-228.
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Family
Caesalpiniaceae
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Scientific Name
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Description
Species Description - Branched, cinerous shrub to 2 m. Leafstalk 1.5-4 cm with a dome-shaped, sometimes bristle-tipped gland between lower leaflet pair; petiole .5-1.5 cm; leaflets 3-6(-8) pairs, sessile, linear, subterete to flat, 1-2.5 cm, 1.5-2.5 r. Stipules minute, deciduous. Flowers 4-8 in small axillary racemes clustered towards branch tips. Pedicels slender; sepals unequal, the longer 5 mm; corolla yellow, nearly regular, 1.5-2 cm diam; stamens 10, unequal. Legume dehiscent, short-stipitate, oblong, flat, 4-8 cm long, .8-1 cm wide, glabrous. Seeds numerous.
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Discussion
C. chatelainiana Hort. p.p. CN n = 14 (rare); n = 28, predominant, numerous determinations; n = 21 ('42/2'), triploids, several determinations (Randell, 1970, based on Australian populations). Reports from other parts of the world 2n = 56 (Irwin and Turner, 1960), n = 28 (Tandon and Bhat, 1970) indicate introductions to be polyploids. Cassia artemisioides is one of a xeric Australian complex including, among species introduced into the United States, C. artemisioides, C. eremophila, C. sturtii, C. helmsii, C. phyllodinea and C. circinata. Symon (1966) characterizing it as a group of some taxonomic complexity, mentions intermediates between most of its members, and describes a hybrid swarm between C. artemisioides, and C. sturtii. But he provides an orderly and ostensibly reasonable taxonomic interpretation. Randell’s (1970) interpretations are devastating. Her conclusions seem to be that several, or most, of the so-called species are but conceptual constructs and have little reality in nature. For example (p 79-80): “In most of the populations examined, several morphological forms occur together . . . Pure populations, comprising only a single taxon are rare. In most cases the recognizable taxa are connected by an extensive and almost complete range of intermediates . . . There is usually no obvious ecological separation of morphological forms in mixed populations . . . Other reproductive isolation mechanisms are presumably also weak.” Some species (C. sturtii, C. desolata, and C. eremophila var. coriacea) are viewed as catchalls of hybrid origin and “may be the product of more than one parental combination.” Tetraploids are predominant, but all morphological types include presumably ancestral diploids. Triploids are characteristic of some species and varieties, these, exhibiting frequent bivalent formation, suggest that basic x = 14 is secondarily derived. Outbreeding and apomixis (pseudogamous adventitious polyembryony), with competing sexual and asexual embryos are characteristic of a reproductive system that has rendered possible extensive adaptive radiation in the arid regions occupied. “While many of these complex populations are found as regeneration after disturbance . . . Robert Brown collected putative hybrid forms in 1803 (33 years before the first permanent settlement in South Australia), and F. Mueller noted morphological intergradation in Cassia in the early years of settlement in the colony (1863)”. Thus, this evolutionary situation is not a recent response to human disturbance, but a long-standing biological structure which has probably evolved over time as a consequence of successful reaction to increasing aridity in Australia. United States material relates to the above in that a few specimens evade Symon’s (1966) classification: my variants 1 and 2 of C. eremophila and some apparent intermediates between C. artemisioides and eremophila. But the bulk of the not uncommon C. artemisioides is reasonably consistent in the United States and specifically distinguishable from its xeric congeners. Probably this happy situation owes to the fact that our cultivated stock derives from relatively few introductions, a limited sample of that existing in nature. Whatever the impact of Randell’s (1970) studies on the classification of this group in Australia may be, Symon’s (1966) taxonomic treatment is effective for those transported to the United States.
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Distribution
S Arizona, common in residential plantings, and urban California, occasionally elsewhere under glass. Cult, ornamental. Nov.-April. Australia, widely cult, in drier, warm regions.
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