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Melaleuca micromera, leaves in different ontogenetic stages II; a, b juvenile transitional leaves; b longitudinal section as marked in a; c–f mature scale leaves; c shoot axis and inserted mature scale leaves; d cross section of a shoot axis and inserted mature scale leaves as marked in c; e basal part of a mature scale leaf (cross section as marked in c); f distal part of a mature scale leaf (cross section as marked in c). (AT abscission tissue, C cuticle, CO cortex of shoot axis, E epidermis, LT leaf trace, OG oil gland, PP palisade parenchyma, P phloem, S stoma, SC sclerenchyma, SP spongy parenchyma, T trichomes, VB vascular bundle, X xylem)
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Key message
In Melaleuca minutifolia mature leaves are linear, in Melaleuca micromera scale-like and peltate. This peltation is caused by swollen basal mesophyll without meristematic fusions. Thus, a novel peltation strategy is described.
Abstract
The foliar change of two Australian Melaleuca species (Myrtaceae) was investigated in different ontog...
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Objective: This research was to investigate acetylcholinesterase inhibitory (AChEI) activity of the essential oil from Myrtaceae and its components. Materials and Methods: The essential oils were extracted from a fresh leave of Myrtaceae plants: Eucalyptus globulus Labill (Eucalyptus), Melaleuca cajuputi Powell (Samed-Khao), Melaleuca citrina (Curt...
Citations
... The oil glands in most Myrtaceae primary tissue are small (45-54 μm) lysigenous cavities (e.g. Dörken and Parsons 2018). In Melaleuca alternifolia, leaf glands can be from 80 to 150 μm in diameter (List et al. 1995), and in the pith of two eucalypts from 91 to 200 μm (Carr and Carr 1969). ...
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.
... The oil glands in most Myrtaceae primary tissue are small (45-54 μm) lysigenous cavities (e.g. Dörken and Parsons 2018). In Melaleuca alternifolia, leaf glands can be from 80 to 150 μm in diameter (List et al. 1995), and in the pith of two eucalypts from 91 to 200 μm (Carr and Carr 1969). ...
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.
Open access Link: https://doi.org/10.1071/BT23007
... The leaf is the organ most easily affected by environmental changes and can best reflect the functions of plants and their adaptability to the environment [5,[10][11][12]. As they are the main carbon source of plants, changes in functional traits of leaves play an irreplaceable role in adapting to environmental stress [13][14][15][16]. Regardless of gymnosperms or angiosperms [17][18][19][20], specific leaf weight increases with increasing tree age, which may be due to the vulnerability of the leaves of older trees to water stress [21][22][23]. ...
Populus pruinosa Schrenk has the biological characteristics of heteromorphic leaves and is a pioneer species for wind prevention and sand fixation. The functions of heteromorphic leaves at different developmental stages and canopy heights of P. pruinosa are unclear. To clarify how developmental stages and canopy height affect the functional characteristics of leaves, this study evaluated the morphological anatomical structures and the physiological indicators of leaves at 2, 4, 6, 8, 10, and 12 m. The relationships of functional traits to the developmental stages and canopy heights of leaves were also analyzed. The results showed that blade length (BL), blade width (BW), leaf area (LA), leaf dry weight (LDW), leaf thickness (LT), palisade tissue thickness (PT), net photosynthetic rate (Pn), stomatal conductance (Gs), proline (Pro), and malondialdehyde (MDA) content increased with progressing developmental stages. BL, BW, LA, leaf dry weight, LT, PT, Pn, Gs, Pro, and the contents of MDA, indoleacetic acid, and zeatin riboside had significant positive correlations with canopy heights of leaves and their developmental stages. The morphological structures and physiological characteristics of P. pruinosa leaves showed more evident xeric structural characteristics and higher photosynthetic capacity with increasing canopy height and progressive developmental stages. Resource utilization efficiency and the defense ability against environmental stresses were improved through mutual regulation of each functional trait.
... Ontogenetical changes in an organism are those changes which can be observed as they develop through different life stages and are changes that are affected by the environment. [14] The late-eluting compounds observed on GC by Southwell and Russell [13] have not been observed in the analysis of the mature tea tree leaves. This indicates that there may be some ontogenetical changes which have not been defined in tea tree. ...
Melaleuca alternifolia (tea tree), family Myrtaceae, is endemic to the northern rivers of NSW, Australia. Since 1925, the volatile components of the hydro‐ and steam‐distilled oils of the leaves have been studied in detail. However, the less‐volatile compounds have not been investigated. Using an ethanolic extract of the seedling leaves, the non‐volatile components were studied using gas chromatography‐mass spectrometry (GC/MS) and liquid chromatography‐ mass spectrometry (LC/MS). Four of these less‐volatile components were isolated by preparative‐HPLC from young seedling leaves and identified as the acylphloroglucinols 1‐(2,6‐dihydroxy‐4‐methoxy‐3‐methylphenyl)‐2‐methylpropan‐1‐one, callisalignone A, 1‐(2,6‐dihydroxy‐4‐methoxyphenyl)‐3‐methylbutan‐1‐one and pulverulentone B described here for the first time from M. alternifolia. These compounds change in concentration in the leaf sets as later seedling leaves mature on the seedling.
... In this family, xerophyte shoots have abundant palisade tissues under the epidermis [34][35][36][37][38][39][40][41]; the epidermis itself has a thick, papillose cuticle [28,36,42] and sunken stomata [38,43]. In addition, species that belong to Tamaricaceae have deep roots [32,34,[44][45][46], which represent an adaptation to drought stress [47][48][49]. ...
Myricaria laxiflora (Tamaricaceae) is an endangered plant that is narrowly distributed in the riparian zone of the Three Gorges, along the Yangtze River, China. Using bright-field and epifluorescence microscopy, we investigated the anatomical and histochemical features that allow this species to tolerate both submerged and terrestrial environments. The adventitious roots of Myr. laxiflora had an endodermis with Casparian bands and suberin lamellae; the cortex and hypodermal walls had lignified thickenings in the primary structure. In the mature roots, the secondary structure had cork. The apoplastic barriers in stems consisted of a lignified fiber ring and a cuticle at the young stage and cork at the mature stage. The leaves had two layers of palisade tissue, a hyaline epidermis, sunken stomata, and a thick, papillose cuticle. Aerenchyma presented in the roots and shoots. Several Myr. laxiflora structures, including aerenchyma, apoplastic barriers in the roots and shoots, were adapted to riparian habitats. In addition, shoots had typical xerophyte features, including small leaves, bilayer palisade tissues, sunken stomata, a thick, papillose cuticle, and a hyaline epidermis. Thus, our study identified several anatomical features that may permit Myr. laxiflora to thrive in the riparian zone of the Three Gorges, China.
Key message
We examined the leaf structure of two basal Cupressus species with a distinct leaf dimorphism. Some foliar features are regarded as ancestral and it is suggested that drought adaptation was one of the important ecological drivers in the evolution of the Cupressus genus.
Abstract
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.
Key message
We examined leaves of a suite of microphyllous woody plants and describe a little-known form of leaf peltation for the first time and also investigate strongly reflexed leaves in two distantly related lineages.
Abstract
Plants cope with a range of environmental conditions, especially related to water relations, and have developed an array of physiological and structural solutions to maintain a functional water balance. There has been considerable recent work on physiological solutions to water deficit but little attention paid to leaf characteristics. In many species there is a change in leaf form from seedlings to adults. We examine such changes in several small-leaved species from the distantly related Asteraceae and Myrtaceae, some of which develop micropeltate or reflexed leaves as adults. All are native to dry or seasonally dry sites. Three major morphological groups were recognised as follows: (1) leaves erect, nonpeltate and scale-like (Ozothamnus hookeri), (2) leaves erect and peltate (Phaenocoma prolifera, Regelia inops), (3) Leaves reflexed (Olearia lepidophylla, Ozothamnus scutellifolius, Ozothamnus reflexifolius, Melaleuca diosmifolia). The microphyllous peltation in P. prolifera and R. inops in the absence of a meristematic fusion/bridge differs from typically peltate leaves. These small-leaved taxa occur in open, high light environments which are very different from the mesic, shaded understorey habitats of typical peltate-leaved plants. Many small-leaved species have leaves closely appressed to the stem and often with recurved margins. The erect leaves are functionally similar to reflexed leaves. Environmental filtering leads to superficially similar plant forms that may have somewhat different ontological origins. Such morphological forms are examples of convergent evolution in distantly related species but within each family are likely phylogenetically related.
The foliar shift from juvenile needle leaves to the mature scale leaves was investigated in five Callitris species. Their habitats range from rainforest to the semi‐arid. In C. macleayana from the most mesic environment the change from needle to scale leaves is variable and juvenile leave are even retained on mature trees. In the other four species there is a rapid change in size and structure to scale leaves. Anatomically the photosynthetic tissue is condensed and stomatal area is limited compared to species with conventional leaves. A hypodermis is most prominent on the abaxial side of the leaves and may play a role in protection from high solar radiation as most species grow in high light areas. While stomata in the four taxa from wet or moderate rainfall areas are freely exposed, those of C. gracilis from semi‐arid habitats are well protected in longitudinal furrows between the decurrent leaves. The reduced leaf area of all species allows close association between the water‐conducting xylem and the stomata that will facilitate rapid leaf conductance. This links with the anisohydric physiology of the genus and the shallow rooting that can take advantage of brief rainfall events for species in arid climates.
