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Published In: Corollarium Bryologiae Europaeae 101. 1856. (Coroll. Bryol. Eur.) Name publication detail

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The Hookeriaceae are a large and diverse, primarily tropical or subtropical, family. There has been considerable controversy over the makeup of the Hookeriaceae, primarily due to the presence of a large number of generic pairs that have very similar gametophytes but radically different sporo-phytes. Crosby (1974b), emphasizing sporophytic similarity, restricted the family to those genera having a hookeriaceous peristome: exostome teeth with broad median furrow, densely and closely striate on lower dorsal surface; endostome basal membranes high, segments broad, strongly keeled, not or weakly perforate, cilia absent. Buck (1987, 1988, 1998) narrowly restricted the Hookeriaceae to include only members of the Hookeriales with a weak stem central strand, elimbate leaves with large, lax cells, and weak or absent costae, smooth setae, and cross-striate exostome teeth. Most gen-era treated here in the Hookeriaceae were positioned by Buck (1987, 1988, 1998) in the Pilotri-chaceae. His treatment of that family emphasized gametophytic similarities and included genera with either a daltoniaceous or hookeriaceous peristome. Buck placed genera in the Pilotrichaceae that usu-ally had a stem sclerodermis, lacked a stem central strand, and had leaves with strong, double costae. Buck et al. (2003) evaluated the Hookeriales using a combination of molecular and morphological techniques. This study restricted the Hookeriaceae to the ecostate genera Crossomitrum and Hooke-ria, and a large Pilotrichaceae again consisting of most of the genera here placed in the Hookeriaceae.

Whittemore and Allen (1989) also examined the Hookeriaceae problem from a gametophytic perspective. They noted that the different peristome morphologies within the Hookeriales were correlated with important functional differences: hookeriaceous peristome xerocastique, i.e., reflexed when dry and incurved when wet; daltoniaceous peristome hygrocastique, i.e., incurved when dry and outcurved when wet. They concluded, on the basis of their observations, that the daltoniaceous peristome did not exhibit uniform morphology. In addition, because of the lack of correlation within the Hookeriales between characters of the peristome and gametophytic features, they considered the daltoniaceous peristome to have arisen more than once in the order. In their view the Hookeriaceae represented a group of mosses with usually bicostate leaves (rarely ecostate); rhizoids unbranched (occasionally sparsely and irregularly branched) and densely clustered abaxial to the leaf insertions; axillary hairs 2(–3) cells long; plants always branched; stem cortex weakly pigmented; and mitrate, usually lobed, calyptrae. The circumscription of the Hookeriaceae and disposition of genera proposed by Whittemore and Allen (1989) is followed here.

An outstanding feature of many genera in the Hookeriaceae is the presence of a massive annulus that consists of 5–20 rows of yellowish, quadrate to hexagonal cells separating from the capsule along a basal dehiscent zone and persistent on the operculum. This feature was first noted and described by Buck (1992) for Philophyllum tenuifolium and Leucomium strumosum. Buck was unsure whether the feature had an annular or opercular origin, and he found these cells were thin-walled on the outer sur-face, thick-walled on the inner surface, and had 1–3 elongate, rib-like thickenings on the inner anti-clinal and periclinal walls. This distinctive annulus occurs in Brymela, Callicostella, Crossomitrium, Lepidopilidium, Lepidopilum, Philophyllum, Stenodictyon, Thamniopsis, and Trachyxiphium. As noted by Buck (1992), it is also found in the Leucomiacae. The gametophytes of most species of the Hookeriaceae often display a remarkable degree of variation. At times this variation is associated with leaf dimorphism, but at other times it appears to be environmentally induced, due to growth in very wet, low light intensity places. When plants that normally have dimorphic leaves are also affected by environmental conditions, the resulting morphological variations can be astounding. As a result of this incredible variability, keys to genera as well as keys to species often fail to adequately separate the taxa. The following key is primarily based on the key to the genera of Pilotrichaceae in Buck (1998).


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 Plants small, medium-sized, or robust in pale green, green, golden, or reddish mats or tufts. Stems prostrate, ascending, or pendent, often complanate-foliate, sparsely or 1–2-pinnately branched, lightly pigmented when young, becoming reddish with age; stems in cross section with hyalodermis or sclerodermis, firm-walled cortical cells, central strand typically absent, occasionally rudimentary to weakly developed; branch primordia scattered over the stems or in leaf axils, typically with scale leaves, occasionally with foliose or subfoliose pseudoparaphyllia; axillary hairs 2(–3) cells long, hya-line or with the basal cell pigmented; rhizoids from clusters of initials abaxial to the leaf insertions, smooth, reddish brown, not or sparsely and irregularly branched. Leaves monomorphic or dimorphic, with often asymmetric lateral leaves larger than the symmetric dorsal and ventral leaves, lanceolate to broadly ovate or obovate; costae double, variable in length but usually long and ending above mid-leaf, occasionally absent; margins usually serrulate or serrate, occasionally dentate or entire, often with a border of elongate cells; cells isodiametric, hexagonal, elongate-rhomboidal, rectangular, or linear,smooth, papillose, or prorate; alar cells not differentiated. Gemmae often produced on stems, typ-ically from clusters of initials abaxial to the leaf insertions. Autoicous, synoicous, or dioicous. Game-tangia on short lateral branches on stems or branches. Setae long or short, smooth, papillose, or spinose. Capsules erect or inclined; exothecial cells often collenchymatous; stomata rudimentary, 2–6-celled, on neck; opercula conic-rostrate; annuli often massive, of 5–20 rows of yellowish, quadrate to hexag-onal cells separating from capsule along dehiscent zone at base, persistent on the operculum; peris-tome diplolepideous: hookeriaceous (exostome teeth narrowly triangular with broad median furrow, densely and closely striate below, coarsely papillose above, dorsal surface dark red, ventral surface hyaline to yellowish, lightly papillose; endostome as high as the exostome, yellowish, lightly papil-lose, basal membranes high, segments broad, strongly keeled, not or weakly perforate, cilia absent or rudimentary) or daltoniaceous (exostome teeth very narrowly triangular, median furrow absent, dorsal surface broad, whitish yellow, lightly papillose throughout, trabeculae thin, median line faint, ventral surface narrow, 1/3 or less the width of the dorsal surface, red or yellow, lightly papillose, deposition thick; endostome as high as the exostome, pale yellowish, papillose throughout, basal membranes high, segments broad, concave-keeled, not perforate, cilia absent or rudimentary). Calyptrae mitrate or campanulate-mitrate, often lobed or laciniate-fringed at base, often variously hairy, often papillose-roughened.


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