Stem anatomy of Apioideae (Apiaceae): effects of habit and reproductive strategy

Apioideae is the biggest and the most diverse of four subfamilies recognised within Apiaceae. Except for a few, likely derived, woody clades, most representatives of this subfamily are herbaceous. In the present study, we assessed stem anatomy of 87, mostly therophytic and hemicryptophytic, species from at least 20 distinct lineages of Apioideae, and juxtaposed them with 67 species from our previous anatomical projects also focused on this subfamily. Comparing our data with the literature, we found that wood anatomy does not allow for a distinction between apioids and their close relatives (Azorelloideae, Saniculoideae), but more distantly related Mackinlayoideae differ from Apioideae in their perforation plate type. Vessel element and fibre length, and vessel diameter were positively correlated with plant height: phenomena already reported in literature. Similar pattern was retrieved for vertical intervessel pit diameter. Wood ground tissue in apioids ranges from entirely fibrous to parenchymatous. The shortening of internodes seems to favour the formation of parenchymatic ground tissue, whereas the early shift to flowering promotes the deposition of fibrous wood in monocarpic species. These results support a hypothesis on interdependence among internode length, reproductive strategy, and wood ground tissue type.

New dicotyledonous woods from the San Carlos Formation (Upper Cretaceous) in Northern Mexico

We describe two new fossil woods from the San Carlos Formation (Upper Cretaceous), Chihuahua State, Mexico. The first wood resembles the fossil genus Metcalfeoxylon in having solitary vessels, scalariform perforation plates, vessel-ray parenchyma pits of similar size as the intervessel pits, axial parenchyma apotracheal diffuse and diffuse in aggregates, and heterocellular multiseriate rays with long, uniseriate tails. The second wood is a new fossil genus, and it is characterized by having diffuse porous wood, vessels predominantly solitary, vessel outlines oval and tending to be of two diameter classes, simple perforation plates, minute alternate intervessel pits, vessel-ray parenchyma pits similar to intervessel pits in size and shape, vasicentric tracheids, non-septate fibers, homocellular rays, and exclusively uniseriate and biseriate rays. This combination of features supports its placement in Myrtales (?Myrtaceae), in a new fossil-genus named Lazarocardenasoxylon. These two new records provide more information about the floristic composition of the Late Cretaceous flora of the San Carlos Formation and its relationship with those from the southern USA. However, a definitive picture of the floristic relationship of these Cretaceous floras of northern Mexico and southern USA remains elusive.

Differences of the stem vascular system across populations of two tropical species under contrasting water conditions

Structural differences in the secondary vascular tissues among habitats can contribute to understanding species performances, especially regarding water and photosynthate transport. The pattern of association between the secondary xylem tissue and water availability from the environment has been widely studied, unlike the secondary phloem, which has been barely explored. Here, we evaluated the structural variation of the secondary xylem and phloem in stems of four populations of two tropical tree species under contrasting water conditions. We also investigated the mirrored structure between both tissues. At dry sites, Moquiniastrum polymorphum had higher vessel density, thicker xylem fibers cell walls, and taller rays in both tissues commonly associated with safe transport, in agreement with our expectations. In contrast, the populations of Zanthoxylum rhoifolium had most features in disagreement with the water availability of each site. The perforation and sieve plates, the ray composition, and the axial parenchyma were similar in the two tree species’ xylem and phloem tissues. However, the quantitative descriptors of cell sizes were not correlated between the xylem and phloem. In general, there is a different pattern of morphological variation across sites in the two tropical tree species, highlighting that any generalization regarding the vascular system structure across environments should be avoided. Xylem and phloem revealed a mirrored structure in a few qualitative features, not followed by the dimensions of different cell types. Future research needs to explore the causes of the unexpected structural variation in the vascular system across populations in tropical tree species.

Cell-wall fluorescence highlights the phases of xylogenesis

The monitoring of xylogenesis makes it possible to follow tree growth responses to stress factors in real-time, by observing the course of wood cell division and differentiation. Proper microscopy techniques are of key importance to exactly identify the xylem cells during the different phases of differentiation. We aimed to apply epifluorescence microscopy to follow the lignification process during the different phases of xylogenesis in Mediterranean softwood and hardwood. Microcores from trees of Pinus halepensis Mill. and Arbutus unedo L. were collected at a site in southern Italy, during the period June-December. Fluorescence imaging of sections stained with a water solution of safranin and Astra blue clearly highlighted the contrast between lignified and un-lignified tissue. The proposed methodology is useful to quickly and unambiguously detect the different stages of cell differentiation, as well as the progress in the lignification process. Moreover, it proved to be easily applied to demanding wood materials, such as Mediterranean woods and can be helpful to better track stress responses and the development of anomalies during wood formation, such as intra-annual density fluctuations.

Characterization of ground parenchyma cells in Moso bamboo (Phyllostachys edulis–Poaceae)

Ground parenchyma cells play a crucial role in the growth and the mechanical properties of bamboo plants. Investigation of the morphology of ground parenchyma cells is essential for understanding the physiological functions andmechanical properties of these cells. This study aimed to characterize the anatomical structure of bamboo ground parenchyma cells and provide a qualitative and quantitative basis for the more effective utilization of bamboo. To do this, the morphology of ground parenchyma cells in Moso bamboo (Phyllostachys edulis) was studied using light microscopy and field-emission environmental scanning electron microscopy. Results show that various geometric shapes of ground parenchyma cells were observed, including nearly circular, square, long, oval, and irregular shapes. Cell walls of both long and short parenchyma cells exhibited primary wall thickening and secondary wall thickening, resulting in a primary pit field and simple pits. Most long cells were strip-shaped (L/W = 2.52), while most short cells were short and wide (L/W = 0.59). The proportion of long cells was 11 times greater than that of short cells. Most long cells were filled with starch grains, and some short cells also occasionally had starch grains. These findings allowed the first construction of the three-dimensional structure of parenchyma cells.

Structure of the secondary xylem and development of a cambial variant in Serjania mexicana (Sapindaceae)

The lianas in the family Sapindaceae are known for their unique secondary growth which differs from climbing species in other plant families in terms of their cambial variants. The present study deals with the stem anatomy of self-supporting and lianescent habit, development of phloem wedges, the ontogeny of cambial variants and structure of the secondary xylem in the stems of Serjania mexicana (L.) Willd. Thick stems (15–20 mm) were characterized by the presence of distinct phloem wedges and tangentially wide neo-formed cambial cylinders. As the stem diameter increases, there is a proportional increase in the number of phloem wedges and neo-formed vascular cylinders. The parenchymatous (pericyclic) cells external to phloem wedges that are located on the inner margin of the pericyclic fibres undergo dedifferentiation, become meristematic and form small segments of cambial cylinders. These cambia extend tangentially into wide and large segments of neoformations. Structurally, the secondary xylem and phloem of the neo-formed vascular cylinders remain similar to the derivatives produced by the regular vascular cambium. The secondary xylem is composed of vessels (wide and narrow), fibres, axial and ray parenchyma cells. The occurrence of perforated ray cells is a common feature in both regular and variant xylem.

Comparative wood anatomy of 15 Malagasy Diospyros species (Ebenaceae)

Diospyros L. (Ebenaceae) is an important source of ebony, a precious wood used for several economically important timber products. Species are overexploited in many regions, including Madagascar, for both the national and international trade, but little is known about their wood anatomy, despite its importance for forensic identification. Wood anatomy has a major role to play in ensuring the sustainable and equitable utilization of Diospyros species that are not threatened by extinction, and in law enforcement to protect threatened species from illegal logging. This study aims to identify, describe, and test the usefulness of anatomical features to support a taxonomic revision of the genus in Madagascar and to enrich databases for wood identification. Ninety-nine wood specimens were collected from the various bio-geographical regions of Madagascar, representing 15 endemic species (twelve previously described and three new) of large trees (reaching DBH ⩾ 20 cm and/or height ⩾ 20 m) were investigated. Standard methods for wood anatomical studies were used. Statistical analysis of the data using Factorial Analysis on Mixed Data was performed for 14 wood anatomical characters. Detailed descriptions and comparisons of the wood anatomy of the 15 species are provided, along with a wood identification key. Analyses showed that all the characters are highly significant () in the separation of the species studies.

Cedroxylon shakhtnaense (Blokhina 2010) Dolezych, Mantzouka et L.Kunzmann comb. nov.; A fossil Abies wood from the late early Miocene Mastixioideae flora of Wiesa (east Germany)

We describe the first evidence of fossil Abies wood from the late early Miocene fossil plant assemblage of Wiesa in east Germany. The comparatively well-preserved piece of xylitic wood was recovered in the kaolin quarry at Hasenberg hill in Wiesa. The Wiesa assemblage is characterized as being allochthonous and partly parautochthonous mass deposits of diaspores, leaves, and wood. The latter component is rather incompletely studied so far. The described fossil is characterized by high rays, mostly uniseriate bordered pits, generally thick and pitted horizontal and tangential ray cell walls, but also partly smooth horizontal ray cell walls, absence of ray tracheids, the occurrence of traumatic resin canals, and rare occurrence of axial parenchyma of two types. This type of fossil wood has been described as Abietoxylon shakhtnaense Blokhina from the Oligo-Miocene of Sakhalin, Russia. Due to nomenclatural issues of Abietoxylon a recombination to Cedroxylon Kraus emend. Gothan is proposed following common practice for affiliation of abietoid fossil wood of Cenozoic age. Cedroxylon shakhtnaense comb. nov. shares anatomical characteristics with the wood of extant Abies Mill., in particular with sections Abies and Grandis, and is most closely related to section Grandis. The properly preserved fossil wood from Wiesa provides the opportunity of applying qualitative and quantitative analyses for testing and discussing its placement in relationship to intra-tree variability and ontogenetic aspects. The first evidence of fossil wood of Abies from Wiesa confirms again the presence of the genus in mid-latitude subtropical zonal vegetation during the beginning of the Miocene Climatic Optimum.

Anatomical characterization of Chimonobambusa quadrangularis based on circumferential and radial variation patterns in cross-sections

The anatomical structure of the bamboo stem is characterized by vascular bundles comprising the xylem, phloem, and sclerenchyma fibrous sheaths as well as parenchymatous ground tissue in which the vascular bundles are embedded. The composition of the stem is the main factor influencing the anatomical characteristics of circular bamboo, which shows considerable variation in the radial direction. However, most species of Chimonobambusa have square stems. Here, we tested the hypothesis that circumferential variation exists in the cross-sectional anatomy of this species. We analysed fibre morphology and the cross-sectional structural characteristics of vascular bundles of Chimonobambusa quadrangularis (Fenzi) Makino and their associated circumferential and radial variation in cross-sections. Microscopic observations were conducted to identify, measure, and compare fibre morphology and the structural characteristics of vascular bundles, including both circumferential and radial anatomical variation. Vascular bundles occurred as undifferentiated, semi-differentiated, and open types in the radial direction with no changes in the circumferential direction. The average length, width, and ratio of fibre length to width were 1463.6 μm, 12.3 μm and 119.3 in the corner region, and 1452.7 μm, 12.8 μm, and 111.3 in the side region, and there were significant circumferential and radial differences in length, width, and the ratio of fibre length to width (). The circumferential variation in density of vascular bundles, the ratio of fibre length to width, radial to tangential diameter ratio of vascular bundles, and the proportion of sclerenchyma were greater in the corner regions than the side regions. The variation in fibre width and the proportion of parenchyma were greater in the corner regions than in the side regions. The density of vascular bundles and proportions of sclerenchyma were greater in the outer stem compared to the inner stem, whereas the length, width, and ratio of fibre length to width were greatest in the centre compared to the inner and outer zones. Circumferential variation of the density of vascular bundles, fibre length and fibre width occurred in the central and outer stem zones. These findings confirm that there are significant anatomical variations in both the circumferential and radial directions and provide a scientific basis for the rational use of Chimonobambusa quadrangularis.