Levenhookia R.Br., Prodr. Fl. Nov. Holland.: 572. 1810

Wege, Juliet A., 2020, Styleworts under the microscope: a taxonomic account of Levenhookia (Stylidiaceae), PhytoKeys 151, pp. 1-47 : 1

Levenhookia R.Br., Prodr. Fl. Nov. Holland.: 572. 1810

Leeuwenhoekia , orth. var.: C.P.J. Sprengel, Anleit. Kenntn. Gew. ed. 2, 2(1): 300. 1818.

Levenhoekia , orth. var.: E.G. Steudel, Nom. Bot. 1: 477. 1821.

Leeuwenhookia , orth. var.: H.G.L. Reichenbach, Consp. Regn. Veg.: 91. 1828.

Leuwenhoekia , orth. var.: F.G. Bartling, Ord. Nat. Pl. 149. 1830.

Leeuwenhockia , orth. var.: E.G. Steudel, Nom. Bot., edn 2(2): 21. 1841.

Leeuvenhookia , orth. var.: F.J.H. von Mueller, Fragm. 1(1): 18. 1858.

Leewenhoekia , orth. var.: F.J.H. von Mueller, Syst. Census Austral. Pl: 86. 1882.

Coleostylis Sond. in J.G.C. Lehmann, Pl. Preiss. 1(3): 391. 1845. Lectotype, here designated: Coleostylis preissii Sond. [= Levenhookia preissii (Sond.) F.Muell.]

Coleostyles , orth. var.: G. Bentham & J.D. Hooker, Gen. Plant. 2(2): 535. 1876.

Type.

Levenhookia pusilla R.Br.

Description.

Diminutive annual herbs with simple or branched stems, usually glandular-hairy. Leaves scattered (rarely basally clustered), usually petiolate, margins entire. Inflorescence racemose, often corymbose or umbellate, sometimes reduced to a solitary flower, with a bract subtending each flower. Flowers bisexual, sometimes protandrous, zygomorphic. Calyx lobes 5, free (rarely with the anterior pair basally connate), margins entire. Corolla lobes 5, connate into a short to long tube with 4 spreading or distally recurved lobes and a smaller, highly modified labellum; labellum ventral or sometimes dorsal (rarely lateral) through rotation of the pedicel, galeiform (hooded), often ornate, covering the distal portion of the column, springing backwards or opening when stimulated to release the column; corolla outgrowths forming a column sheath at the throat, often nectariferous. Column immobile or with restricted movement upon release from the labellum; anthers 2, bilocular, pollen yellow; stigma 2-lobed. Ovary inferior, with many ovules on a free-central placenta. Nectary sometimes present on top of the ovary. Capsules dehiscent. Seeds small, brown, rugulose, sometimes papillate.

Number of species, distribution and ecology.

A genus of 12 species from a variety of habitats in southern temperate Australia, extending into the arid zone in Western Australia and the Northern Territory (Fig. 1A ). The only representative of the genus in Tasmania is currently listed as extinct in that State (refer to the additional information provided under L. dubia ). Some species are disturbance opportunists that are more readily found the year following a fire.

Floral morphology and pollination.

The hooded labellum is responsive to touch, usually springing backwards through rapid recurvature of its claw, releasing the column (Fig. 2A, D, F, H, I ) before gradually repositioning itself at or above the level of the corolla lobes (Fig. 2B, E ); it does not enclose the column or respond to stimuli again. Levenhookia dubia is an exception since its sessile labellum opens to release the column, but does not otherwise move (Fig. 2J, K ). As first noted by Erickson (1958), the exact point of stimulus varies amongst species: probing the apex of the hood or apical appendage will trigger the release of the column in L. dubia , L. leptantha , L. murfetii , L. octomaculata , L. pusilla and L. stipitata , whereas the labellum in L. aestiva and L. pauciflora is more reliably stimulated by touching the basal appendages. Erickson (1958) observed the sensitive point to be in the throat of the flower in L. preissii , something which I intermittently observed in L. aestiva . Sometimes the labellum cannot be manually triggered and it has been hypothesised that flowers await a certain stage of maturity before becoming responsive ( Sargent 1918; Erickson 1958). In the absence of an external stimulus, growth of the upper-most stigmatic lobe, or apparently of the column itself, can sometimes trigger labellum movement ( Erickson 1958).

The action of the labellum usually results in a degree of column movement (Fig. 2D, F, H, K ), although movement is slight or lacking in both L. murfetii (Fig. 2I ) and L. pusilla . These small-flowered species appear to be autogamous: the anthers dehisce within the labellum and the stigmatic lobes develop concurrently, becoming covered in pollen ( Sargent 1918; pers. obsv.). In L. leptantha , L. aestiva and L. dubia , the column moves from the anterior to the posterior side of the flower, coming to rest against the column sheath at the base of the corolla lobes (Fig. 2D, F, K , respectively) before gradually shifting to an erect or slightly forward-arched position that maximises display of the stigmatic lobes (Fig. 2B, E ). In L. aestiva , the column is long, free from the corolla tube and held under tension in untriggered flowers, moving rapidly when released from the labellum and coming to an abrupt stop when it hits the sheath. This catapult-like mechanism results in pollen being sprayed outwards from the anthers (and presumably onto a pollinator). In this species, the stigmatic lobes mature once pollen has been shed, thereby promoting outcrossing or geitonogamous self-pollination. The stigmatic lobes in L. pauciflora , L. preissii and L. pulcherrima similarly appear to mature once pollen has been shed.

In L. leptantha , the column is adnate to the anterior side of the corolla tube, with only the short (0.7-1.1 mm long), distal portion free to move. Despite this, a catapult-like action is still achieved. The distal portion, which is slightly forward-arched and therefore held under a degree of tension by the labellum, moves rapidly to the opposite (posterior) side of the flower when the labellum is triggered, with its forward momentum apparently halted by its attachment to the anterior side of the corolla tube (the posterior rim of the column sheath may also act as a stopper). Like L. aestiva , pollen is sprayed outwards from the anthers, but may also spill onto the lower stigmatic lobe which, in contrast to L. aestiva , develops before the upper one and usually while the column is still enclosed by the labellum. The lower stigmatic lobe, which is strongly upturned, can often be seen protruding from the labellum and this may enable it to receive pollen from a visiting insect. The upper stigmatic lobe matures once the column has been exposed from the labellum and is prominently displayed to promote outcrossing. Staggered development of the stigmatic lobes is also evident in L. chippendalei , L. dubia , L. octomaculata and L. stipitata , of which L. dubia is akin to L. leptantha in having the column adnate to the corolla tube (a trait also shared with L. pauciflora , L. pulcherrima and possibly L. sonderi ).

Levenhookia pauciflora has a distinct column morphology that generates a unique movement. In addition to adhering to the corolla tube, the column is attached to the anterior side of the column sheath, which further restricts its movement upon release from the labellum. Its distal end (Fig. 2H ) is sharply angled towards the labellum and has a dilated tip subtended by a weak hinge. The hinge provides the tip with a degree of flexibility that may enable direct placement of pollen on an insect. Erickson (1958) noted that this species produced "a veritable shower" of pollen when triggered; however, I observed its column to move comparatively slowly into a nearly upright position without generating an obvious spray of pollen, although some pollen was transferred to the prominent tuft of hairs at the apex of the labellum, potentially functioning as a form of secondary pollen presentation.

Erickson (1958) suggested that the release of the column from the labellum in Levenhookia results in geitonogamous self-pollination via the catapulting of pollen between flowers on the same plant. This is at odds with my own observations, which indicate that the flowers are usually too widely spaced and pollen is not flung far enough for this to occur. Furthermore, in some species ( L. dubia , L. pauciflora , L. octomaculata and L. stipitata ), I observed little to no pollen spray; however, further observations are warranted, particularly given the suggestion that the column is held under increasing tension as the flower matures ( Erickson 1958: 206). This suggests that variation is to be expected when studying flowers within a population or even on the same plant.

The interaction between the labellum and the column, which is difficult to investigate in the field given the size of the plants and the rapidity of the movements, remains incompletely studied. Observations are lacking for many species and pollination records are largely wanting. Erickson (1958: 203) noted woolly bee-flies actively probing flowers of L. leptantha , noting that pollen grains were "sprayed about the head and under the body". I have only made two incidental observations: a small native bee on L. pulcherrima (at J.A. Wege 1937), moving rapidly between flowers while foraging for pollen and a large wasp repeatedly visiting L. octomaculata (at J.A. Wege 2074), although it was unclear whether it was transferring pollen between flowers.

Other notes.

Erickson (1958: 200) notes that Levenhookia flowers close at night by folding the four main corolla lobes together. I have observed this phenomenon in L. aestiva , L. dubia , L. leptantha and L. octomaculata ; however, this trait is not universally exhibited, with the small flowers of L. murfetii and L. pusilla remaining open.

Mildbraed (1908) recognised three sections based on labellum and column sheath morphology (at which time only six species were recognised). A revised infrageneric classification will be considered once a robust molecular phylogenetic framework is available, although this is unlikely to be warranted given the size of the genus.

Figures

Figure 1. Levenhookia is a genus of annual herbs endemic to Australia A distribution in temperate and semi-arid regions of Australia, scale bar 1000 km B L. leptantha (J. A. Wege 2063) C L. pusilla (J. A. Wege 1749 & W. S. Armbruster) D L. octomaculata (J. A. Wege 2074) E L. pulcherrima (J. A. Wege 1937). Photos by J. A. Wege.

Figure 2. Labellum and column movement in Levenhookia. Black arrow = labellum hooded over column; white arrow = labellum ' triggered' to release column; yellow arrow = labellum repositioned following column release; blue arrow = column position immediately following release from labellum A L. stipitata (unvouchered, Augusta area, Western Australia) B L. aestiva (J. A. Wege 2090) C-E L. leptantha (J. A. Wege 2063), with labellum enclosing the column (C), triggered to release the column which moves to the opposite side of the flower (D) and subsequently repositioned (E) with the stigmatic lobes developed F L. aestiva (J. A. Wege 2090), labellum triggered with column momentum stopped by the sheath at the base of the corolla lobes G, H L. pauciflora (at J. A. Wege 1071 & C. Wilkins): note the unusual, distally-angled column and brush-tipped labellum I L. murfetii (J. A. Wege 2060): note the dorsal position of the labellum; J, K L. dubia, with the labellum opening (but not otherwise moving) to release the column (K). Photos by R. W. Davis (A, B) and J. A. Wege (C-K).