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The genera of Leguminosae-Caesalpinioideae & Swartzieae

L. Watson and M.J. Dallwitz

Petalostylis R. Br.

Petalogyne F. Muell., Petalostyles Benth,

Type species: P. labicheoides R. Br.

Habit and leaf form. Xeromorphic shrubs; subequal, leaves and inflorescences crowded on ‘short shoots’; armed (with spine-like rachides), or unarmed.

Phyllotaxy distichous. The leaves compound and ostensibly simple; when not unifoliolate, pinnate, or bifoliolate (progressing on the shoots from imparipinnate to bi- and unifoliolate); imparipinnate. The leaflets small, many per leaf; opposite or sub-opposite, or alternate; petiolulate; without noticeably twisted petiolules. Stipules absent or early caducous or very inconspicuous in mature leaves (narrow, very caducous); not connate. Stipels absent.

Inflorescence and floral morphology. The flowers solitary.

The flowers hermaphrodite; not pentamerous throughout; departing from pentamery in the androecium; coloured. Floral tube length relative to total hypanthium + calyx length about 0.25. Hypanthium present to absent, the androecium hypogynous; very short. The perianth comprising distinct calyx and corolla. Calyx 5; covering the rest of the flower in bud; polysepalous; more or less regular; members imbricate. Corolla present; slightly irregular; 5; without greatly reduced members; spreading, polypetalous. Petals sessile; imbricate-ascending; yellow. Disk present and conspicuous. The androecium comprising 5 members; members all free of one another; members markedly unequal; including staminodia. The staminodia 2; with acuminate imperfect anthers, smaller than the fertile stamens, opposite the adaxial sepals. Fertile stamens 3 (opposed to the abaxial sepals). Anthers attached at the base of the connective; dehiscing longitudinally. Ovary sessile or subsessile; free (the style naviculate, petaloid, saccate, three lobed with the middle one longer and terminated by the small stigma). Ovules few, or numerous (rarely).

Fruit, seed and seedling. Fruit a two-valved pod; straight; valves twisting and enrolling during dehiscence; oblong-linear, plano-compressed, not becoming woody. The mature valves without prominent venation. Seeds endospermic; arillate (the arils cupular, enveloping the bases of the seeds); with a straight or slightly oblique radicle; amyloid-negative. Cotyledons flat; of Type 2; epigeal.

Transverse section of lamina. Leaves with conspicuous phloem transfer cells in the minor veins. Druses absent from the mesophyll. Mesophyll secretory cavities absent. Adaxial hypodermis absent. Leaf girders absent. Laminae dorsiventral. Mesophyll without unaligned fibres or sclereids. Minor veins mainly with abundant accompanying fibres.

Leaf lamina epidermes. Epidermal crystals not seen either adaxially or abaxially. Simple unbranched hairs common; scabrid. No compound or branched eglandular hairs seen. Capitate glands not seen. Hooked hairs present. Cassieae-type leaf pseudo-glands not seen. Expanded and embedded hair-feet absent. Basally bent hairs present. Adaxial: Adaxial interveinal epidermal cell walls straight in optical section; conspicuously pitted; medium-thin. Stomata adaxially very rare. Abaxial: Abaxial stomata not predominantly paracytic (mixed anomcytic, anisocytic, actinocytic, tetracytic). Abaxial epidermis not papillate. Abaxial interveinal epidermal cell walls straight, or gently undulating; not conspicuously pitted in optical section; staining normally with safranin; of medium thickness.

Pollen ultrastructure. Tectum reticulate; finely to moderately regularly reticulate. Length of colpi greater than one half pole to pole distance. Foot layer of pollen wall with obvious projections.

Cytology. Basic chromosome number, x = 14. 2n = 28.

Species number and distribution. 2 species (P. cassioides, P. labicheoides). Australia.

Tribe. Cassieae.

Miscellaneous. Illustrations: • P. cassioides: FloraBase. • P. labicheoides: Florabase. • P. labicheoides, e.m. scanned pollen (Graham & Barker, 1981).


We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, and classification. See also Guidelines for using data taken from Web publications.


Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1993 onwards. The genera of Leguminosae-Caesalpinioideae and Swartzieae: descriptions, illustrations, identification, and information retrieval. In English and French. Version: 22nd March 2017. delta-intkey.com/caes’.

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