Philip Ladd

Context
Parasitic plants are widespread throughout the global flora and have diverse lifestyle strategies. In most cases these plants are detrimental to the host but may have some beneficial effects on the co-occurring plants in the sourrounding communities. Some have large macroscopic plant bodies and can photosynthesise, and are therefore able to produce some fixed carbon but do take water and nutrients from the host, especially if aerially attached. Very few species have vegetative parts completely enclosed in the host, having only reproductive structures externally displayed. Whether such internal parasites have as severe effects on the host as parasites with macroscopic plant bodies is unclear.

Aims
The endoparasite Pilostyles hamiltoniorum infests pea species (predominantly Daviesia species) in the south-west of Western Australia. We investigated the effect of this parasite on the vegetative growth and reproduction of Daviesia angulata in heathland vegetation.

Methods
Size, flowering and fruiting of parasitised and unparasitised host plants were recorded in three 6 × 30 m plots in a revegetated gravel pit in the Jurien Bay area of Western Australia.

Key results
A proportion of 21% of host plants was parasitised and these were significantly taller than unparasitised plants. These plants had 52% fewer flowers on average than unparasitised plants and subsequently far fewer fruits.

Conclusions
The reduction in reproductive output by this internal parasite was at least equal to or more severe than occurs in published examples of decreased productivity of other species parasitised by species with macroscopic plant morphology.

Implications
The reduced reproductive output of the host plants would be inimical to seed stores in the soil that this species relies on for regeneration after fires that commonly affect the vegetation in this region.

Leaves are the photosynthetic organs of most plants. However some species have other photosynthetic structures as well as leaves or have lost the ability to produce green leaves and have evolved alternative organs for carbon fixation. The Fabaceae is a speciose family that has species with probably the widest range of photosynthetic structures in land plants. We examined five pea species where leaves are often ephemeral or have been entirely reduced to nonphotosynthetic bracts to understand the ways in which alternative structures have been formed. The evolutionary incentive to use stems for photosynthesis is likely related to light and seasonal water availability. Cytisus scoparius sheds leaves under dry conditions and photosynthesis is then restricted to ridged stems where the ridges are derived from highly modified stipular tissues. In Genista sagittalis the annual shoots do have leaves but the stems form extensions derived from leaf bases that laterally expand to form continuous leaf-like wings down the stem increasing photosynthetic area. Anatomically Cytisus and Genista are relatively mesomorphic and avoid water stress by losing leaves (Cytisus) or having annual stems (Genista). The other three species grow in a mediterranean-type climate with pronounced summer drought. Leaf blades are reduced to brown bracts but the leaf bases extend between the stem nodes to form photosynthetic ridged stems or cladodes. Jacksonia alata is a diminutive species with limited photosynthetic area which may contribute to its subordinate position in its community. Leptosema aphyllum and L. tomentosum have much broader cladodes and are larger shrubs. These three species have stems and cladodes with a dense anatomical structure and abundant sclerenchyma that allow the species to take advantage of the winter-spring rainfall but enable their survival through the hot and arid summer. The five species emphasise that different structures can be modified to achieve a similar outcome.

Leaves of seed plants were evolutionarily derived through syngenesis (fusion) of the photosynthetic cylindrical axes of the earliest land plants and subsequent morphological diversification. However, in some later evolved taxa leaves became very reduced or entirely lost and photosynthesis was again restricted to stems. Reduction of photosynthetic area to stems is mostly found in plants from arid environments and is generally considered disadvantageous in competition for light with plants with leaves but may be useful if water is limiting. For taxa that cannot form normal leaves on adult plants, increasing photosynthetic area is only possible by modification of other plant parts. Some taxa produce leaf-like phylloclades that are developmentally different from leaves. We investigated Jacksonia floribunda and J. anthoclada (Fabaceae) leaves and phylloclades. In all Jacksonia species true leaves are only developed in the earliest ontogenetic stages, and subsequently are reduced to minor, nonphotosynthetic brownish scales. After several nodes on the seedling, photosynthetic phylloclades, each inserted in the axil of a scale, form the foliage. Immature phylloclades have vestigial nonphotosynthetic leaves borne on small projections from the edge of the blade. These soon abscise. The phylloclades are flattened branches and when mature have a distinctly reticulate venation and a sinuous margin with alternating mucronate tips where the vestigial leaves were attached. Jacksonia species demonstrate a transformational series where in most species foliage is reduced to branchlets. In a few others branchlets are winged forming cladodes or are condensed and laterally expanded to form phylloclades. Our findings on the more derived species in Jacksonia illustrate the complexity of plant morphological responses to evolutionary pressures of seasonal water limitation.

Species in the family Proteaceae are almost invariably tetramerous with the stamen adnate to a tepal. Andromonoecious inflorescences bearing many male flowers composed of a single (spathuloid) stamen and a female flower with a pubescent stigma, as in Endobeuthos paleosum, are unknown. We suggest that the specimen is a bisexual flower with scores of stamens surrounding a single stigma-style. Further, the specimen is too old to fit with current understanding of the migratory history of the Proteaceae.

The majority of taxa with peltate leaves are perennial herbs native to swampy or aquatic habitats or to mesic shaded understorey habitats. These large peltate leaves are formed by a meristematic bridge at the lamina–petiole junction. However, there are also several strong-light exposed, small-leaved, xero- and scleromorphic Myrtaceae with leaf peltation which is formed without a meristem fusion/bridge. Here, abaxial laminar tissue at the insertion point of the petiole forms a basal extension, so that a weak peltation occurs. This shifts the petiole onto the adaxial laminar surface. The formation of micropeltation in Myrtaceae leads to erect leaves that are strongly appressed to the shoot axis and the entire foliate, vertical shoots appear as “green columns”, a result that is also the case in taxa with reflexed minute leaves. It seems that micropeltation achieves the same goal as leaf reflexion in small-leaved taxa—reduction of heat-load and transpiration during the hottest phases of the day by a lower light interception at midday compared to the morning and evening. Thus, physiologically micropeltation and reflexion of minute leaves seem to be the result of convergent evolution.

Instead of leaves, in a few species the main photosynthetic organ is a flattened structure that can be a modified branch (e.g. Ruscus, Jacksonia) or a fused combination of branch and leaf tissue (e.g. Phyllocladus) called a phylloclade. The phylloclades of Phyllocladus lack xeromorphic features in their wet habitat. They are broad under the low light conditions as are those of Ruscus which can occur in forest understories. However Ruscus is also common in dry habitats and shows numerous xeromorphic features. In Jacksonia extensive sclerenchyma and thick cuticle protect the phylloclades from desiccation damage in xeric seasonal conditions. Despite former contrary definitions of phylloclades we advocate they be defined as pseudo-petiolate organs determinate in growth which arise from axillary buds in the axil of reduced leaves and resemble a leaf.

Context
The Southwest Australian Floristic Region has exceptional plant evolutionary complexity for fire, nutrition and pollination traits.

Aims
Our aim was to allocate pollination strategies to all vascular plants in this biodiversity hotspot by analysing existing and new data.

Methods
Here we assigned a flower syndrome to ~8800 plants in this region, using floral traits and visitation records for insects, birds or mammals, which were well correlated.

Key results
Specific insect relationships were most common (3383), especially with native bees (2410), including buzz pollination (450). Others were pollinated by wind (1054 plants), water (35) or had relatively unspecialised flowers visited by diverse insects (3026). Specific associations with flies (588) or butterflies and moths (165) were less common. Approximately 14% were primarily pollinated by birds (601) or birds and insects (583) – with much larger flowers (corresponding with bird bill lengths), and less insect-attracting colours (e.g. red or green). Non-flying mammals, especially honey possums, visit certain flowers along with birds. Pollination complexity peaked in the Myrtaceae (11% bird, 25% bird and insect), Fabaceae (2% bird, 46% bee, 2% buzz pollination) and Proteaceae (40% birds, 31% specific insects). Bird pollination also has multiple origins in the Ericaceae (8%), Haemodoraceae (20%), Rutaceae (16%), Pittosporaceae (14%) and Eremophila (45%). Extreme specialisations included secondary pollen presentation (1231), post-pollination colour change (72), mobile columns (310), explosive pollen release (137) and visual (209) or sexual (171) deception in orchids. Pollination trait complexity included >275 evolutionary transitions, especially from insects to birds (130), more specific insects (100), or wind (15). These followed similar morphological pathways within families but differed between them.

Conclusions
This complexity appears to be globally unique, and peaks in highly speciose plant families with diversity centred in the region.

Implications
This has ecological and genetic consequences, especially for rare flora management, ecosystem restoration and assessing plant vulnerability to habitat degradation, fire and climate change.

Context. Most tissues of Myrtaceae plants have oil glands. The anthers of many species have an oil-containing apical gland that is larger than those in other tissues of the plant.

Aims. Representative species in the family were examined for the diversity of gland form and their oil contents.

Methods. Representative anthers were sectioned for light microscopy and scanning electron microscopy study and anthers from selected species were analysed for oil content.

Key results. The most common gland form is globular and narrowly attached to the apex of the connective, but in members of certain tribes, the gland is completely enclosed in the connective. The greatest morphological diversity is in the Chamelaucieae. Anther glands vary from plesiomorphic globular forms to glands that are larger than the anther thecae and almost completely fill the connective.

Conclusions. There are three possible functions for the glands, including the following: (1) protecting the anthers from herbivores, (2) mixing with the pollen to aid adhesion to stylar hairs on many Chamelaucineae, and (3) rewarding pollinators that use the oil–pollen mixture as food. Implications. It is generally considered that the oils in various tissues of the Myrtaceae deter herbivores. In Myrtaceae with abundant anthers, the glands could deter flower visitors from consuming the anthers. Gland oil of the Eucalyptus and Leptospermum species examined contained α pinene as did the leaves of all species examined. The gland oil composition in Chamelaucium uncinatum and Verticordia grandis that have pollen presenters was different from that in the leaves and also different from that in the anthers of the two Verticordia species where bees collect the pollen–oil mixture for food.

Brood pollination is one of the more unusual ways in which plants reproduce. The plant has to trade off damage to its flowers and reduction in future offspring in exchange for the production of seeds. Brood pollination occurs along a continuum from parasitism to mutualism. In two closely related monocot species of Thysanotus in southwest Western Australia one autogamous species is parasitised by visiting beetles that eat the ovules and affect viable seed production. In the other species, which is normally buzz pollinated, visiting beetles can be facultative brood pollinators. In many cases, adults of brood pollinator mutualisms feed on nectar or more rarely pollen. The Thysanotus system is unusual, as the anthers of T. manglesianus are poricidal so pollen is not freely accessible to the beetle which is incapable of sonication and no nectar is produced. However the beetles damage the flowers and consume some pollen, which is necessary as the pollen will not be available unless the anther walls are breached. A beetle may lay an egg on a plant's ovary, where the hatched larva burrows through the ovary wall and eats the developing ovules. However, not all flowers receive an egg despite the flower being visited by beetles. Thus, when there is no bee pollinator, beetle visitation allows seed to be produced, albeit less than would be produced if the beetles were absent and a normal pollinator present. As this type of pollination interaction is unknown in other species of Thysanotus, it is not possible to decide if the brood pollination mutualism has developed from a parasitic relationship or the reverse. The autogamous species does not need a pollinator and always had a higher fruit set and fewer beetles than the population of the other species at a site where the more usual bee pollinator was absent. It may be that brood pollination mutualism is a development from a parasitic relationship.

Leaf morphology and anatomy of two Cupressus species, C. nootkatensis and C. vietnamensis, were investigated with classical paraffin technique and scanning electron microscopy (SEM). Like all Cupressus species these two are characterised by a dramatic change in the foliage. Juveniles have needle leaves first before they change abruptly to the mature scale leaf type. In C. vietnamensis, needle-leaved shoots occur next to scale-leaved ones even on mature trees, which is unique among today´s Cupressus species. Adults of C. nootkatensis develop only scale leaves throughout. In both taxa, the scale leaves show a distinct dimorphism between lateral and facial leaves, which are arranged in a flat spray; the foliate shoots are two-dimensionally flattened. These scale leaves show several xeromorphic features; e.g. strongly reduced leaf size, stomata with high, collar-like Florin rings, the presence of a distinct hypodermis as a continuous layer and well-developed transfusion tissue. The needle leaf type is found in Cunninghamia which is the basal member of the Cupressaceae and so is regarded as the ancestral condition and scale leaves as a derived one. Scale leaves are found in all the members of the cupressoid clade even within the basal taxa from mesic habitats. However scale leaves are a preadaptation to survival under xeric conditions and they are likely an evolutionary driver of the radiation of Cupressus into arid environments, as has also been the case in genera such a Callitris.