TWO NEGLECTED ASPECTS OF FOSSIL CONIFERS

Most conifers, living and fossil, drop their foliage in one of two natural ways. Either each leaf is abscised separately, or intact leafy shoots are abscised. Thus, a fossil leafy shoot of a leaf-dropping species is an unusual specimen, and is the result of premature, violent removal, as by storm. Any reproductive organs it bears are likely to be immature. This idea, applied to the ovules of Taxus jurassica Florin leads to their reinterpretation: they prove unlike Taxus, but rather, like Amentotaxus. A few living conifers drop their leaves or leafy shoots at the end of each summer. There may be evidence that a fossil was deciduous. Phyllotaxis has seldom been examined closely in fossil conifers but can be clearly observed even in compressed specimens. Three main kinds occur: 1) Leaves or cone scales are attached singly in a helix (spiral) which is usually very regular. 2) Leaves are attached two (or more) at a node and those of the next node alternate strictly; if there are pairs, the next pair is at 90° decussation. 3) Leaves are in opposite pairs but the next pair is at an angle of less than 90°, and the leaves form a double helix or bijugate spiral. In fossils all three kinds can be subdivided according to the numbers of oblique rows (parastichies) rising to the right and left, in relation to the diameter of the organ. Torreya gracilis Florin (from the Jurassic) proves to have the same phyllotaxis, a double helix, as that found in modern Torreya shoots. But Florin's Taxus jurassica has its leaves in decussate pairs, unlike Taxus, but rather, like Amentotaxus. For this and other reasons it is here renamed Marskea jurassica (Florin) comb. cnov.     

Phyllotaxis in two species ofRubia,R. akane andR. sikkimensis

Phyllotaxis and vascular course in the vegetative shoots ofRubia akane andR. sikkimensis were studied. Each node of both species has a whorl of four leafy members among which two are true leaves. Arrangement of the true leaves is not decussate but bijugate, i.e., opposite leaves are arranged spirally. Bijugy was ascertained not only by gross morphology but also by arrangement of primordia around the shoot apex and vascular course through several internodes. Divergence angle differed widely with internodes even within a single shoot and with shoots even in the internodes which are separated by a same number of nodes from the apex. Mean divergence angles obtained for five youngest internodes of some shoots were between 49.4° and 61.8° inR. akane and between 53.6° and 59.4° inR. sikkimensis. Young seedlings ofR. akane showed decussate phyllotaxis in the lowermost several internodes. In the internodes near the lower end of the bijugate part, the divergence angle was wider than in the upper internodes. The directions of the phyllotactic spirals in the main axis and the lateral branches were either homodromous or antidromous, and those in the oppositely paired branches also were either homo- or antidromous.     

Hormonal effects on phyllotaxis ofEuphorbia lathyris L.

Benzyladenine and gibberellic acid sprays (100 mg/l) onEuphorbia lathyris L. plants were absolutely successful (100% of the plants) in inducing a change in its normal decussate phyllotaxis. Benzyladenine produced a change to tetracussate, tricussate and bijugate, and gibberellic acid to spiral phyllotaxis. Benzyladenine and gibberellic acid treatments resulted in a significant increase in apex diameter (72.8% and 19.1% respectively). CCC, Ancymidol, Alar and Glyphosine did not alter decussate phyllotaxis.     

Shoot development ofAucuba japonica I. Morphological study

The shoot development ofAucuba japonica was studied morphologically. The shoot shows dichasial branching in connection with the formation of a terminal inflorescence and shows a decussate phyllotaxis even in the reproductive phase. The sequence of initiation of successive foliar appendages is very precise, hence the foliage leaf, scale leaf and bract can be compared with each other even at their stages of initiation. In the stage of proximal foliage leaf formation the shoot apex is flat, while in the stage of formation of distal foliage leaves, bud scales and proximal bracts, it becomes concave. In the stage of formation of distal bracts the apex becomes domed. Plastochron durations are relatively long in the vegetative phase in comparison with other plants, and the duration from initiation of the first pair of appendages to that of the second is about one and a half months. Both male and female inflorescences exhibit basically a thyrsoid type of monotelic synflorescence.     

LEAF DEVELOPMENT IN ISOPHYLLOUS AND FACULTATIVELY ANISOPHYLLOUS SPECIES OF PENTADENIA (GESNERIACEAE)

Shoots of Pentadenia orientandina exhibit varying degrees of anisophylly, ranging from pairs of equal-sized leaves to pairs of large ventral and small dorsal leaves. In this study we compare phyllotaxis, leaf expansion, and accompanying histological changes in extremely anisophyllous shoots of this species and in isophyllous shoots of the related species, P. crassicaulis. In P. orientandina, decussate phyllotaxis is modified at leaf initiation, and angles of leaf insertion appear to be further changed during leaf expansion. In both species, leaf primordia of a pair are not distinguishable at inception, suggesting an equivalent developmental potential. In P. orientandina, size differences between ventral and dorsal leaves become significant at the P2 or P3 stage, coincident with lamina initiation. Minute dorsal leaves are arrested in their development at the P3 stage and mature without differentiation of multiple epidermis, stomata, mesophyll and most vascular tissue. Variation in dorsal leaf structure in P. orientandina emphasizes the plasticity of leaf development in this facultatively anisophyllous species.     

The architecture of Zeylanidium olivaceum (Podostemaceae) inferred from the structure of the primary shoots

Zeylanidium olivaceum (Podostemaceae-Podostemoideae) is the only crustose-rooted species of the genus that still develops prominent primary shoots from the seedling in addition to the secondary (root-borne) shoots forming the clonal plant body. The primary shoots are articulated into an up to 8.5 cm long and 4 mm thick stalk (hypocotyl) and a copiously foliated paint-brush-like shoot which is sympodially branched in the form of a helicoid cyme. The helicoid branching pattern indicates a transversal prophyll position, typical of the dicotyledons, but replaced in most other Podostemoideae by a median prophyll position. The short stems within the leafy head do not separate, but are fused to a dense aggregate (coenosome). Branches are mainly vegetative with a rosette of about 20 elongate subulate leaves. The primary shoots branch in the vegetative stage and thus differ from other Podostemoideae where ramification is confined to the floriferous shoots. The leaves adhere together at the base, forming an apical furrow-like hollow surrounding the shoot tip. The tiny shoot apex is one-layered, radially symmetrical, and develops leaf primordia in a decussate pattern. The erect primary shoots thus differ from the distichously foliated plagiotropic secondary shoots by the decussate phyllotaxis, and by the presence of more than 20 leaves on a shoot as compared to the about six leaves on the vegetative and floriferous secondary shoots. The features observed in the primary shoots are interpreted as primitive as compared to those of the secondary shoots. Z. olivaceum is thus characterised by heterobathmy, i.e., the occurrence of plesiomorphic (primary shoots) and apomorphic features (secondary shoots). The primary shoots exhibit primitive features that apparently have been lost in secondary and primary shoots of most other members of subfamily Podostemoideae.     

LEAF DEVELOPMENT AND PRIMARY VASCULAR ORGANIZATION IN SHOOTS OF ANISOPHYLLEA DISTICH A

Anisophyllea disticha is characterized by strong shoot dimorphism. Orthotropic shoots with helically arranged scale leaves produce tiers of plagiotropic shoots, while plagiotropic shoots are anisophyllous and bear dorsal scale and ventral foliage leaves arranged in a unique tetrastichous system. In this study we compare the patterns of leaf development and primary vascular organization in the two types of shoots. Orthotropic shoots have an open vascular system with five sympodia. Expansion of orthotropic shoot scale leaves occurs from P1 to P10–12, and leaf tissues mature precociously. Plagiotropic shoots have a closed vascular system with six sympodia. Leaves in ventral and dorsal orthostichies do not differ significantly in size until ca. P15, but ventral leaves are distinct histologically from the second node in an orthostichy, P4–6. Ventral foliage leaves have a diffuse plate meristem, and leaf expansion continues until ca. P30. Differentiation of ventral and dorsal leaf trace procambium parallels the divergent patterns of leaf expansion. These observations demonstrate the strong correlation among shoot symmetry, leaf development, and vascular differentiation within dimorphic shoots of one species.     

Biochemical Systematics of Gymnosperms (3)—On the Systematic Position of Tax aceae from Their Seed Protein Peptides and Needle Peroxidases

The major peptides in the seed of Taxus and Pseudotaxus have molecular weight about 31, 22 and 20 kilodaltons (Kd) shown by SDS polyacrylamide gel electrophoresis. The seed protein peptides of Cephalotaxus is very similar to those of Taxus and Pseudotaxus except a few bands of high molecular weight. Some considerable differences in peptide pattern exist between Amentotaxus and the three genera cited above. The former has a new major peptide, 33K, but lacks 22 K. The seed of Torreya does not contain peptide 44 K, although Torreya and Amentotaxus have many bands in common. To a certain extent, the seed protein peptides of Podocarpus nagi are similar to those of the above taxa. A great range of divergency in needle peroxidases among different genera of Taxaceae has been observed by using electrophoresis, while the zymogram of Cephalotaxus is somewhat similar to that of Taxus. Two series of protein data demonstrate, that there is an evolutionary tendency from Taxus to Torreya through Pseudotaxus and Amentotaxus within Taxaceae. And the Taxaceae is closely related to Cephalotaxus by way of Taxus. The systematic positionof the Taxaceae, therefore, should be placed under the Coniferales.     

Photomorphogenesis and phyllotaxis during vegetative growth in Sinapis alba and Xanthium strumarium

Abstract The effect of light on the rate of formation of leaf primordia was investigated at the apex of seedlings of Sinapis alba and Xanthium strumarium. It was found that light accelerates this rate. On the other hand, no significant light effect was found on the angles of divergence of successive leaves during the transition from the almost decussate leaf position of the cotyledons to the helical phyllotaxis of the stem leaves. In fact, light and dark grown plants use the same leaves for the transition from decussate to helical phyllotaxis. Thus, if time is plotted in ‘biological units’ (number of primordia) there is no difference between light and dark grown plants. Using scanning electron microscope techniques it was found that the ‘primordia free apical area’ enlarges during development. The rate of enlargement is accelerated by light. However, if time is expressed in biological units (number of primordia) no difference between light and dark grown plants exists. It is concluded that light accelerates the realization of the apical pattern without interfering with the specification of the pattern. In other words, light accelerates the development of an apex without affecting the temporal and spatial coordination of the events.     

Formation of Pseudowhorls inPeperomia verticillata(L.) A. Dietr. Shoots Exhibiting Various Phyllotactic Patterns

Pseudowhorls are composed of leaves attached at almost equallevels and separated by single fully elongated internodes. InPeperomiaverticillata, pseudowhorls form regularly in shoots exhibitingboth spiral and truly whorled patterns of phyllotaxis. In spiralsystems, they are composed of successive leaves positioned onthe ontogenetic helix. In whorled phyllotaxis, leaves of twoadjacent whorls occur at almost the same level and this wayform a pseudowhorl. The number of leaves per pseudowhorl dependson the type of phyllotactic pattern and also the system of primordiapacking. In all the shoots, regardless of the type of phyllotaxis,the number of leaves per pseudowhorl equals the number of leafprimordia in physical contact with the apical dome. It is thesame as the higher number in contact parastichy pairs in spiralpatterns or the number of orthostichies in whorled phyllotaxis.The pseudowhorled pattern is already manifested in the arrangementof leaf primordia. In spiral and whorled phyllotaxis the plastochronratio calculated for primordia or whorls belonging to adjacentpseudowhorls is always higher than that calculated for membersof one pseudowhorl. Moreover, angular distances between primordiaof one pseudowhorl in spiral patterns are more uniform thanexpected in Fibonacci phyllotaxis. These observations were madeon plants both growing in pots and culturedin vitro. 6-Benzylaminopurine,a synthetic cytokinin, added to the medium increases the meannumber of leaves per pseudowhorl. It seems that this effectis indirect: phyllotaxis changes first rather than the destinyof a particular internode in a process of selective elongation.Copyright1999 Annals of Botany Company Peperomia verticillata, pseudowhorls, phyllotaxis, shoot apex.     

Branching Principles Governing the Architecture of Cornus kousa (Cornaceae)

The complex structure of the crown of Cornus kousa, generallyfive-forked in vegetative branching and two-forked in reproductivebranching, is analysed quantitatively and described by two basicbranching principles: decussate phyllotaxy and the resettingrule for planes of branching. Most Cornus species have opposite,decussate phyllotaxis. The leaf pair (with axillary buds) definesthe branching plane of a node. Because of regular phyllotaxis,the fundamental branching pattern is that every branching planealong an axis is perpendicular to the preceding one. However,the first node of a lateral horizontal shoot always has a horizontalbranching plane; we term this the resetting rule. We observedthat resetting occurs when the first nodes initiated in thevertical plane are repositioned by a twisting of their firstinternodes. All later nodes alternate directions, i.e. showusual decussate alternation. Foliage leaf nodes usually producethree-forked branchings. When vegetative winter buds are formed,a foliar node and adjacent scale leaf node produce a five-forkedbranching. When reproductive winter buds with a terminal inflorescenceare formed, the last foliar node and two adjacent scale leafnodes can produce a variety of branchings but usually producean equal two-forked branching. To understand better the architecturein C. kousa, we contrast it with C. capitata which does notproduce buds with scale leaves and whose vegetative nodes areclearly separated. Copyright 1999 Annals of Botany Company Branching pattern, Cornaceae, Cornus kousa, decussate branching, dogwood, Japanese strawberry tree, tree architecture, tree geometry.     

Leaf Development, Metamorphic Heteroblasty and Heterophylly in Berberis s. l. (Berberidaceae)

Shoot development of temperate and tropical members of Berberis s. l. was examined in order to assess: (1) the homology of the spines along the long shoots and the foliage leaves that form on the short shoots; (2) the occurrence of heterophylly and/or heteroblasty in the genus; and (3) the structural correspondence between cataphylls, spines, and foliage leaves. The 1-5-armed spines have been interpreted as modified compound leaves lacking stipules, as a modified lamina (central spine) with stipules (lateral spines), or less often, as transformed branches, or as epidermal outgrowths. On the other hand, the foliage leaves of the short shoots have been interpreted as leaflets of palmately compound leaves. Our results indicate that there are three distinct leaf types per node: (1) Leaves modified in spines spirally arranged in long shoots; (2) foliage, expanded leaves densely arranged in short shoots; and (3) cataphylls protecting axillary buds. The spines are leaf homologs with a clear distinction between the leaf base with stipules, and a laminar portion modified into the 1-5-armed spine; the lateral spines are not stipules as they arise from the marginal meristem of the laminar portion, and not from the leaf base. The foliage leaves also have stipules flanking the leaf base. Both spiny leaves and foliage leaves develop an articulation between the base and the laminar portion. Cataphylls of the short shoots of Berberis s. str. and those of the reproductive short shoots of Mahonia correspond to the entire leaf base, but those of the renewal (vegetative) shoots of Mahonia are spiny and have an odd vestigial pinnately compound lamina. Heterochrony due to ontogenetic truncation caused by the formation of the terminal inflorescence at the apex of the short shoots could be responsible for the lack of petiole/lamina differentiation in the foliage leaves. The spiny long-shoot/foliose short-shoot system of branching in Berberis s. str. appears to be genetically and phylogenetically fixed and not environment-dependent. This represents a clear example of metamorphic heteroblasty sensu Zotz et al. (Botanical Review 77:109–151, 2011) with further occurrence of heterophylly along the short shoots.     

Experimental and Analytical Studies of Pteridophytes: XXXVIII. Some Observations on Spiral and Bijugate Phyllotaxis in Dryopteris aristata Druce

In an attempt to assess some of the factors which determineleaf arrangement at the shoot apex, a study has been made ofphyllotaxis in the fern Dryopteris aristata. It is shown thatclockwise and counter-clockwise spirals occur with equal frequencyboth in field collections and in adventitious and experimentallyinduced buds which arise on the rhizomes and apices of plantsgrown in the laboratory. In addition to the two common spiralarrangements, a form with bijugate phyllotaxis has been noted.It is concluded that the three types of leaf arrangement arenot under direct genetic control, but rather are dependent oncircumstances of growth at the apex.     

ONTOGENY AND PHYLLOTAXIS OF THE TERMINAL VEGETATIVE SHOOTS OF MICHELIA FUSCATA

Tucker Shirley C. (Northwestern U., Evanston, Ill.) Ontogeny and phyllotaxis of the terminal vegetative shoots of Michelia fuscata. Amer. Jour. Bot. 49(7): 722–737. Illus. 1962.—Two patterns of symmetry occur in Michelia fuscata In the lead shoots, leaves arise in a 2/5 spiral arrangement which may be either clockwise or counterclockwise. Other shoots are dorsiventrally organized; these shoots produce leaves in a modified ½ phyllotaxis in which the angle between the 2 files of leaves lies between 100° and 150°, according to the particular branch. Both types of shoot have a zonate apical meristem with a biseriate tunica a central initial zone, and a peripheral zone. The apical configuration of cells does not change appreciably during the plastochron. The flat to low-convex outline of the shoot apex is maintained by initiation of the leaves close to the summit of the apex; the diameter of the meristem diminishes greatly after such an initiation. Leaf inception in the subsurface tunica layer is followed by precocious activity of the marginal meristems which extend the stipular flanges completely around the base of the apical meristem. The stipular margins then fuse laterally and form a hood over the apex. A subapical initial meanwhile is active in the leaf blade, where it persists up to the time the leaf is 2 mm high. The most recent primordium is 300 μ high before another leaf is initiated. The vascular system of the stem is a cylindrical network of leaf traces, with 6–12 traces per leaf. The procambium develops acropetally from preexisting vascular strands in the stem below. Elements of the diverse sclereid system differ in shape in different tissues, according to the availability of intercellular space. Goebel's term “Pendelsymmetrie” is discussed with reference to apical activity in Michelia.     

Leaf phyllotaxis: Does it really affect light capture?

The intriguing mathematical properties of leaf phyllotaxis still attract scientific attention after centuries of research. Phyllotaxis, and in particular the divergence angle between successive leaves, have been frequently interpreted in terms of maximization of light capture, although certain model simulations of light capture by vertical shoots revealed minor effects of phyllotaxis in comparison with the effect of other morphological features of the plant. However, these simulations assumed a number of simplifications, did not take into account diffuse light, and were not based on real plants with their natural range of morphological variation. This study was aimed at filling these gaps by examining the influence on light harvesting of shoot architecture and divergence angle in four species with spiral phyllotaxis (Quercus ilex, Arbutus unedo, Heteromeles arbutifolia and Daphne gnidium) with a realistic 3-D model (Y-plant). A wide range of divergence angles (from 100° to 154°) was observed within each species, with 144° being the most frequent one. These different divergence angles rendered very different vertical projections of the shoot due to contrasting patterns of leaf overlap as seen from above, but they rendered indistinguishable light interception efficiencies (Ea). Setting the leaves with an opposite-decussate phyllotaxis led, however, to a 40–50% decrease of Ea. The interplay of internode length, leaf size and shape, and leaf elevation angle led to significant species differences in Ea. Thus, only particular phyllotaxis (e.g., decussate) might be functionally inefficient under certain combinations of the various morphological variables that influence light capture of a shoot. This revised version was published online in June 2006 with corrections to the Cover Date.     

Ontogeny of the reproductive shoot apex ofClethra barbinervis,especially on the superficial view

The structure and the ontogenetic process of the reproductive shoot apex forming a terminal inflorescence ofClethra barbinervis were examined, especially concerning the superficial view of the apex. The system of contact parastichies is 2+3 in phyllotaxis in the vegetative phase, changing to 5+8 for bract arrangement in the reproductive phase. At the same time the size of the apex is conspicuously enlarged. The size of the foliage leaf primordia in the vegetative phase is larger than that of the bract primordia in the reproductive phase. The radial cell files, which are clear in the vegetative shoot apex, are not recognizable at least in the early stage of the reproductive phase. The author proposes a close correlation between the appearance of the radial cell files, as well as the construction of the apical sectors, and the sizes of the shoot apex and leaf primordia. It may be proposed also that the construction of the apical sectors is closely correlated with the phyllotaxis.     

Variation in crown light utilization characteristics among tropical canopy trees

BACKGROUND AND AIMS: Light extinction through crowns of canopy trees determines light availability at lower levels within forests. The goal of this paper is the exploration of foliage distribution and light extinction in crowns of five canopy tree species in relation to their shoot architecture, leaf traits (mean leaf angle, life span, photosynthetic characteristics) and successional status (from pioneers to persistent). METHODS: Light extinction was examined at three hierarchical levels of foliage organization, the whole crown, the outermost canopy and the individual shoots, in a tropical moist forest with direct canopy access with a tower crane. Photon flux density and cumulative leaf area index (LAI) were measured at intervals of 0.25-1 m along multiple vertical transects through three to five mature tree crowns of each species to estimate light extinction coefficients (K). RESULTS: Cecropia longipes, a pioneer species with the shortest leaf life span, had crown LAI <0.5. Among the remaining four species, crown LAI ranged from 2 to 8, and species with orthotropic terminal shoots exhibited lower light extinction coefficients (0.35) than those with plagiotropic shoots (0.53-0.80). Within each type, later successional species exhibited greater maximum LAI and total light extinction. A dense layer of leaves at the outermost crown of a late successional species resulted in an average light extinction of 61% within 0.5 m from the surface. In late successional species, leaf position within individual shoots does not predict the light availability at the individual leaf surface, which may explain their slow decline of photosynthetic capacity with leaf age and weak differentiation of sun and shade leaves. CONCLUSION: Later-successional tree crowns, especially those with orthotropic branches, exhibit lower light extinction coefficients, but greater total LAI and total light extinction, which contribute to their efficient use of light and competitive dominance.     

Matter-economical roles of evergreen leaves inAucuba japonica,an understory shrub in the warm-temperate region of Japan

Seasonal dynamics in nitrogen and phosphorus content were examined for each component organ ofAucuba japonica, an evergreen understory shrub in the warmtemperate region of Japan. Evergreen foliage was the largest pool for each nutrient; nitrogen and phosphorus were accumulated and stored in autumn and then redistributed in the spring. For individual leaves, such seasonal accumulations and redistributions were repeated through two or three years and then at leaf fall, an additional amount was withdrawn. Rapid growth of new shoots and flowers during spring was supported by the massive redistribution of the nutrients from the old foliage. The redistribution accounted for 85% and 65% of the total nitrogen and phosphorus input to the new shoots, respectively. Such a high ratio of redistribution resulted in a conservative nutrient economy, and must be positively related to the photosynthetic production in the ligh-limited environment.     

Biflavone of Torreya jackii Chun and Its Taxonomical Significance

Kayaflavone has been isolated from leaves of Torreya jackii Chun, a species endemic to China. Seven species, belonging to Taxus, Pseudotaxus, Amentotaxus as well as Torreya, in Taxaceae were examined for kayaflavone, which has been detected only in the genus Torreya. The result seems to justify the separation of the genus from the others and the establishment of the monotypic tribe, Torreyeae.     

四种裸子植物叶精油化学成分的研究

采用气相色谱—质谱—计算机联用仪对穗花杉、南方红豆杉、三尖杉和罗汉松叶精油化学成分的研究发现,三尖杉和穗花杉叶精油的组成特点极为相似,相同成分１３个,占各自精油组成的４８．０７％和３３．３２％．三尖杉和南方红豆杉叶精油的相同成分４个,占各自精油组成的１６．１４％和４０．５９％．在一定程度上支持三尖杉科和红豆杉科的亲缘关系接近,红豆杉科可能是通过穗花杉属和三尖杉科相联系的观点．罗汉松和穗花杉叶精油的相同成分４个,占各自叶精油组成的比例为２４．０９％和２０．８２％,比罗汉松和南方红豆杉、三尖杉之间组分的相似性要高．反映出罗汉松科和红豆杉科之间有一定联系,穗花杉属是认识红豆杉科、三尖杉科和罗汉松科之间系统关系的关键属