Ixora (Rubiaceae) on the Philippines - crossroad or cradle?

BACKGROUND

The Philippine archipelago is globally one of the most important model island systems for studying evolutionary processes. However, most plant species on this archipelago have not yet been studied in sufficient detail. The main aim of this study is to unravel the evolutionary history and biogeographic relationships of the Philippine members of the pantropical genus Ixora.

RESULTS

The complex plastid and nuclear divergence patterns in Philippine Ixora, documented using tree and network approaches, reveal a highly dynamic evolution in Ixora, involving several phases of radiation and recolonization. Philippine Ixora comprises at least five lineages, of which one is most closely related to species from Wallacea, and the remaining four to species from Asia.

CONCLUSIONS

Our study highlights the importance of Philippine species for understanding phytogeographic patterns in the Indomalayan-Australasian eco-region. The overall genetic differentiation, as well as the incongruence between genealogies based on the biparentally inherited nucleome and the maternally inherited plastome in Ixora, reflect the complex tectonic history of the Philippine archipelago. The Ixora lineage related to Wallacean species supports the delimitation of different ecozones along Huxley's line, because it is absent from Palawan. The remaining four lineages are all allied with Asian taxa, reflecting several waves of colonization. Close relationships between some widespread Philippine species and locally adapted narrow endemics suggest that the widespread, genetically diverse species act as pools for the formation of new species in a process of ongoing speciation. Our results suggest that the species concepts of some of the more widespread taxa need to be revised.

Morphology, anatomy and cytology of critically endangered endemic Asperula daphneola from, West Anatolia, Turkey

Asperula daphneola, which belongs to Rubiaceae family, is only distributed on Nif Mountain. The present study investigates the species anatomically, morphologically and cytologically, laying the basis for future biosystematic studies as well as introducing this endemic taxa. A. daphneola seeds were 1.3-1.8 X 2.3-2.9 mm; ovate; seed surface was prominent and channelled; dorsal type was convex, hispid hairs all over; hylar zone type recessed; yellowish green colour. Type of pollen were stephanocolpate and had 6 colpus with tectate structure. The chromosome number in A. daphneola was counted as 2n=20.

The epidermal cell structure of the secondary pollen presenter in Vangueria infausta (Rubiaceae: Vanguerieae) suggests a functional association with protruding onci in pollen grains

Secondary pollen presentation is a well-known phenomenon in the Rubiaceae with particularly conspicuous pollen presenters occurring in the tribe Vanguerieae. These knob-like structures are formed by a modification of the upper portion of the style and stigma, together known as the stylar head complex. In the flower bud and shortly before anthesis, the anthers surrounding the stylar head complex dehisce and release pollen grains which adhere to the pollen presenter. The epidermal cells of the pollen presenter facing the anthers are radially elongated with a characteristic wall thickening encircling the anticlinal walls of each cell towards the distal end. These cells were studied in the pollen presenter of Vangueria infausta using electron and light microscopy in conjunction with histochemical tests and immunohistochemical methods. Other prominent thickenings of the cell wall were also observed on the distal and proximal walls. All these thickenings were found to be rich in pectin and possibly xyloglucan. The terms “thickenings of Igersheim” and “bands of Igersheim” are proposed to refer, respectively, to these wall structures in general and those encircling the anticlinal walls of each cell near the distal end. The epidermal cells have an intricate ultrastructure with an abundance of organelles, including smooth and rough endoplasmic reticulum, Golgi apparatus, mitochondria and secretory vesicles. This indicates that these cells are likely to have an active physiological role. The pollen grains possess prominent protruding onci and observations were made on their structure and development. Walls of the protruding onci are also rich in pectin. Pectins are hydrophilic and known to be involved in the dehydration and rehydration of pollen grains. We hypothesise that the thickenings of Igersheim, as well as the protruding onci of the pollen grains, are functionally associated and part of the adaptive syndrome of secondary pollen presentation, at least in the Vanguerieae.

Unique calcium oxalate "duplex" and "concretion" idioblasts in leaves of tribe Naucleeae (Rubiaceae)

PREMISE OF THE STUDY

This basic study may help plant biologists better understand the variety and occurrence of crystal forms and their function in plants. Literature records hold four examples of two different crystal types in one cell. One, unillustrated report mentions druses and crystal sand from one species of tribe Naucleeae (Rubiaceae) and "occasional occurrences" in additional unnamed taxa. Here, we surveyed Naucleeae (103 of 179 species, 23 of 24 genera, all seven subtribes) for "duplex idioblast" distribution for systematic significance and describe examples of this rare feature.

METHODS

Cleared, dehydrated, herbarium leaves were mounted unstained in resin. Slides were examined with polarization optics for crystal types and locations, and representative areas were electronically digitized. Scanning electron microscopy and x-ray analysis verified calcium oxalate composition.

KEY RESULTS

Idioblast configurations occur as crystal sand (CS) only (most common, 92 spp.) to CS plus one embedded druse (55 spp.), to CS plus 2-3 druses (6 spp.), to one druse with scanty surrounding CS (a few spp.), to a "naked" druse (16 spp.). Trends occur in some subtribes. A previously undescribed conspicuous, spheroidal calcium oxalate aggregate "concretion" idioblast occurs in only four species of Mitragyna (Mitragynineae). Idioblasts are most common along vascular bundles and in mesophyll, less so only along vascular bundles, and least common only in mesophyll. Tiny "secondary" crystals are common in ordinary mesophyll cells.

CONCLUSIONS

Crystal types appear to be systematic features in Naucleeae. Duplex idioblasts (CS and druses) and aggregate concretions are a demonstration that much is yet to be discovered about crystals.

Elaborate petals in Australian Spermacoce (Rubiaceae) species: morphology, ontogeny and function

BACKGROUND AND AIMS

Australian Spermacoce species display various types of elaborate petals. Their precise morphology, ontogenetic origin, and function are hitherto unknown. The aim of the present paper is to unravel the development and nature of the diverse types of elaborate petals in Spermacoce through a floral ontogenetic study.

METHODS

The floral ontogeny of six species characterized by different types of corolla appendages was studied by scanning electron microscopy and light microscopy. In order to elucidate the possible functions of the elaborate petals, field observations were conducted as well.

KEY RESULTS

Scanning electronmicrographs show that full-grown petals of Spermacoce lignosa, S. phaeosperma and S. redacta bear appendages on their ventral side. Despite their different appearance at anthesis, the appendages develop very similarly in all three species. They are initiated at the same developmental stage and are first visible as two arcs of primordia converging from the upper margins of the petal towards its midvein and downwards. In S. brevidens, S. caudata and S. erectiloba, the full-grown petals have two long, concave protuberances, which develop from the tissue at both sides of the petal's mid-vein. In these three species, initiation of appendages on the ventral side of the petals is also observed, but they are hardly visible on the mature petals. The two types of elaborate petals tightly enclose the anthers, both in bud and during most of the flowering period.

CONCLUSIONS

Among Australian Spermacoce species, two types of elaborate petals can be distinguished. The former hypothesis that the two types of elaborate petals are essentially homologous is here rejected. Field investigations point out that the elaborate petals might play a role in the pollination biology of the species.

A cytological study on Kelloggia (Rubiaceae), an intercontinental disjunct genus between eastern Asia and western North America

A cytological study was carried out for the first time on four populations of the only two species of Kelloggia (Rubiaceae), which occur disjunctly in eastern Asia (K. chinensis Franch.) and western North America (K. galioides Torr.). The consistent mitotic prophase chromosome condensation pattern and interphase nuclei type were determined for both species. The chromosome base number of the genus is suggested to be x = 11. The karyotype of 2n = 22 = 2x = 16m + 6sm was examined for both species. The karyotypical asymmetry of 1A and 2A was found in K. chinensis and K. galioides, respectively. According to the predominant evolutionary direction of karyotype asymmetry in angiosperms, K. galioides (2A) seems slightly more evolved than K. chinensis (1A). Our finding is consistent with the hypothesis of the Old World origin of Kelloggia based on molecular study.

[Pharmacognostical studies on the stem and leaf of Mussaenda pubescens]

Morphological and microscopic chracteristics of Mussaenda pubescens Ait. f, a traditional Chinese medicine were described and illustrated with line drawings. TLC and UV analysis of the medicinal material were also undertaken. These studies provide referential information for identification and development of this medicinal material.