Asteraceae

Queensland

This key covers all 173 genera that have native or naturalised species growing in Queensland. Excluded are genera for which only cultivated species or “formerly naturalised” species are known for Qld. For the vast majority of couplets, a decision can be accurately made based on naked-eye observation or with the use of a 10x hand lens. In Asteraceae, the leaves are highly variable in size, form, and vestiture. The occurrence of entire margins is not random – the whole of Tribe Gnaphalieae (in Queensland) has entire leaves. The occurrence of toothed leaves should be closely checked when using this key – sometimes teeth are only 1 mm long, or teeth may be present on some leaves but not on others. The maximum number of questions required to reach an answer is 19.

Definitions Achene: A single-seeded indehiscent dry fruit with the seed free from the pericarp except at the placenta; the fruit in almost all Asteraceae. Capitulum: An inflorescence consisting of a head of small closely packed stalkless flowers or florets arising on a flattened axis (receptacle). The whole is surrounded or subtended by an involucre of bracts and simulates, in appearance and function, a single large flower (plural capitula). Compound heads: Flower heads that are made up of numerous capitula. In some cases, these heads are spherical and have few or no bracts at the base; otherwise they may be hemispherical or ellipsoidal. They can be recognised by the presence of numerous sets of involucral bracts within the head, each surrounding a group of florets. Florets a) Tubular florets: Typically these florets are bisexual, though sometimes functionally male. In some species tubular florets occupy the entire capitulum; in others they are restricted to the central part of the capitulum. b) Filiform florets: These are usually female (with a style, but no anthers), and with a very slender corolla tube, and reduced corolla lobes. c) Ligulate florets: These are strongly zygomorphic florets where the corolla tube is slit along one side and an expanded limb forms a ligule. A distinction is sometimes made between ligulate florets and ray florets, but they are here treated as synonymous. In some species of the Tribe Gnaphalieae, the upper portion of the involucral bracts is spreading and petal-like; these species never have ligulate florets. Involucral bracts: A series of tightly clustered bracts in one to several whorls, surrounding or subtending the florets and fringing the receptacle. The involucral bracts form the outer part of the capitulum, and as a whole, are called the involucre. Pappus: The pappus is the modified calyx of the Asteraceae. Commonly, the pappus comprises many feathery bristles adapted for wind-dispersal, but the pappus is very diverse and may comprise scales, awns, or a membranous cup. Quite often it is absent. a) Bristles are ± circular or polygonal and have the longer diameter of the cross section no more than 3 times the shorter diameter. The bristles may be smooth or finely to coarsely barbed or plumose. b) Awns are rigid elements with ± circular or polygonal cross sections greater than 100 µm in diameter. Often awns are retrorsely barbed. c) Scales are elements with a "flatter" cross section (i.e. longer diameter more than 3 times the shorter diameter), regardless of relative overall lengths and widths of the elements. A scale may terminate in one or more bristle-like or awn-like appendages; such scales are said to be aristate. Scales may be smooth or ciliate. d) a membranous cup is formed from the fusion of short scales, and is a single ring-like structure, often translucent. [Pappus definitions are taken from the Flora of North America, Volume 19]. Receptacle and paleae: The receptacle is the platform upon which the florets sit. Typically it is flat or slightly convex. It is sometimes pitted or alveolate, and may have the jutting remnants of the connection between the peduncle and each individual floret. In a few genera e.g. Acmella, the receptacle is strongly conical in shape. The surface of the receptacle may bear paleae (in many genera, some or all florets are individually subtended by a bractlet called a palea). Collectively paleae have been called "chaff" and paleate receptacles have been described as "chaffy." Receptacles that bear paleae are referred to as paleate. Receptacles that do not have paleae sometimes bear hairs or setae instead (e.g. many in the thistle group).