The New Flora of the Volcanic Island of Krakatau

Front matter

THE NEW FLORA

OF THE

VOLCANIC ISLAND

Introduction

INTRODUCTION

A quarter of a century ago the small group of islands, Krakatau, Verlaten island, and Lang island, lying in the middle of the Sunda Strait between Java and Sumatra, was the scene of the most violent volcanic outburst of historic times. The three islands enclose an almost circular basin approximately 40 square kilometres [25 sq. miles] in area. Before the terrific explosion, which lasted from August 26th to August 28th, 1883, the northern part of Krakatau which was then 9 kilometres long and 5 kilometres broad [5½ × 3 miles] was separated from the other two islands by narrow arms of the sea. On the south side the peak Rakata rose in the form of a steep cone to a height of 832 metres [2728 feet]; on the slope of this, near the centre of the island, was situated the many-peaked hill of Danan, 400 metres [1350 feet] high, the remnant of an annular crater-wall. Towards the north the hilly region of the Perboewatau, dominated by several small elevations, extended to the coast. The whole island, from the beach to the summit of Rakata, was covered with an impenetrable forest. Verbeek who paid a short visit in July 1880 to the northern part of the uninhabited island, which has since disappeared, found some lava-streams which reached the coast only in the Perboewatan region; these were covered by a sparse vegetation and their surface was but slightly weathered. The lava-streams were probably formed during the only recorded eruption of 1680.

For a long time the island had been regarded as an extinct volcano. On May 20th, 1883, a new crater on Perboewatan suddenly became active, the activity being accompanied by loud explosions which were heard for a considerable distance over Java and Sumatra, and after a few days a large part of the island and a portion of Verlaten island were covered with a layer of ash and pumice to a depth of 1 metre. On the north side of the highest peak, and here and there over the whole of the northern part of Krakatau, stems of trees could still be seen rising above the grey ground as miserable remnants from the former luxuriant forest; while on the south side of the cone, on Lang island and on a fourth island, Poelsche Hoed (Polish Hat), situated between Lang and Verlaten islands, which has completely disappeared since the eruption of August 27th, the vegetation suffered but little.

In June a second crater was formed at the foot of Danan, which threw out ashes and pumice. At the beginning of August a third crater, together with numerous fissures which gave off steam and smoke, appeared on the southern slope of Danan; this was afterwards completely shattered and served as the main crater during the last eruptions.

The outbursts increased in frequency and culminated in the terrible catastrophe of August 26th and 27th, the effects of which were felt over almost the whole surface of the earth. The explosions were heard not only throughout the Malay Archipelago, but also in Ceylon, Burma, Manilla, New Guinea and on the west coast of Australia. At Batavia and Buitenzorg in Java, 150 kilometres [92½ miles] from the scene of the explosion, the noise resembled artillery fire at close range. The vibrations made the window-panes rattle and shook the houses to such an extent that objects were thrown from tables.

During the eruption the volcano covered the whole neighbourhood for a distance of 35 kilometres [22 miles] with glowing stones and hot ashes. Near the centre of activity, on the island of Sebesi, with 2000 inhabitants, villages suffered the fate of Herculaneum and Pompeii. A dense rain of ashes fell over the whole of South Sumatra, to Benkoelen and Palembang in the north, in West Java beyond Batavia and the residency of Preanger, while the finer dust was spread over a much greater area amounting approximately to 600,000 square kilometres [234,000 square miles]. In a south-westerly direction the rain of ashes extended 1200 kilometres [750 miles], and it is well known that the finest particles mixed with aqueous vapour and suspended in the upper region of the atmosphere were carried round the world and caused the wonderful twilight effects which were observed everywhere in December 1883. The total amount of material thrown out from the craters of Krakatau from May to August 1883 was estimated by Verbeek, after careful calculation, at 18 cubic kilometres [4·4 cubic miles]. As a result of this enormous loss of material the chief crater and adjacent parts of the island were undermined and on the morning of August 27th the climax was reached: a large portion of the island and of the surrounding sea-floor fell in like an insufficiently supported vault. The sea was drawn after the débris from all sides into a funnel-like depression and, surging up again over the submerged crater, produced gigantic waves which rose to a height of 40 metres [131 ft.] and, carrying with them blocks of rock which reached 300 cubic metres in bulk, broke repeatedly on the coasts of Java and Sumatra. For a distance of several kilometres inland everything was destroyed; whole villages disappeared and about 30,000 people were drowned. In the shallow Java Sea the waves acquired less force. The low islands in the Bay of Batavia suffered considerable damage and in Tandjong Priok, in the harbour of Batavia, from midday on August 27th for the next 36 hours as many as 18 seismic waves were recorded, the first and highest of which reached a height of more than 2 metres. On the same day large waves were produced in all the harbours of the Indian Ocean where the deeper water furnished much more favourable conditions for their transmission. By August 28th the seismic waves had found their way into the North Atlantic Ocean and were recorded at Rochefort, Cherbourg, Havre and other places.

The geological expedition conducted by Verbeek, which under took the investigation of the group of islands two months after the eruption, found that enormous geographical changes had occurred (see Sketch-map, Pl. II.). The small island Polish Hat, part of Lang island as well as two-thirds of Krakatau itself, embracing an area of 22·85 square kilometres [8·9 square miles], had sunk. The line of fracture passed through the middle of Rakata, the highest peak of which still remained. The face of the mountain from summit to sea-level now formed a steep and almost vertical wall (Plate III.). At the foot of the cliff and beyond in the new area of sea which occupied the site of the former crowded group of islands, the lead touched bottom at a depth of 100, 200 and in places 300 metres.

No lava-flows appear to have occurred during the whole period of volcanic activity, but on the other hand the three islands were covered with pumice and layers of ash reaching on an average a thickness of 30 metres and frequently 60 metres [98—196 ft.]. To this extent Verlaten island and Lang island were increased in height: the former had also increased in circumference.

A new marginal belt was formed along the south-west to the south-east coast of Krakatau, 4·6 square kilometres of land being added to the zone of 10·7 square kilometres which remained. During the short period of two months after the eruption subaerial denudation had already carved out of the loose strata deep valleys and gorges in some cases with vertical walls from 6 to 8 metres high. In the vicinity of the peak, where the newly formed deposit must have been thinnest, patches of the original rock surface protruded here and there exposing the blasted and carbonised remains of tree stems. The last remnants of plant-life which had withstood the first outbursts were everywhere destroyed and buried under a thick covering of glowing stones. The islands, which were formerly green, assumed the appearance of a desert of the most desolate type, a desolation, uninhabited and in all probability for a considerable period uninhabitable, separated by 19 to 25 kilometres [12—15½ miles] from the neighbouring and half-destroyed islands of Sebesi and Seboekoe and by 35 to 45 kilometres [22—28 miles] from the nearest points of the Javan and Sumatran coasts. But the first pioneers of plant and animal life soon obtained a footing and to-day, 25 years since the complete destruction of all organic life on the group of islands, these are again covered with a mantle of green, the growth being in places so luxuriant that it is necessary to cut one’s way laboriously through the vegetation.

Plate II

Map of the Sunda Strait. Scale 1 : 1,750,000. Sketch-map of the Krakatau Islands (after Verbeek). Scale 1 : 200,000.

Part 1

Dr Melchior Treub, the distinguished and genial Director of the Botanical Institute at Buitenzorg in Java, rendered a great service to Science by initiating the study of the new Krakatau flora and thus paving the way for further investigations. The botanical explorations, made on three different occasions, of the islands which were entirely depleted of vegetation in 1883 have not only furnished results of general biological interest, but by demonstrating the successive stages in colonisation, they also afford one of the most important contributions towards the solution of the much discussed problem as to the source and history of the introduction of a flora into an island far removed from the mainland. The older literature concerned with this interesting problem in plant-geography, so far as regards direct observation, deals with the history of colonisation of recently formed coral islands, that is of flat land surfaces, and with the investigation of the means of dispersal of plants from older coral reefs and volcanic islands. On Krakatau, Treub had an opportunity of studying the more complex problem: how a volcanic island, which has lost the whole of its flora as the result of an eruption, acquires a new vegetation; how, in other words, an island of considerable height suddenly emerging from the sea becomes stocked with plants; and further by what successive stages the new floral elements appear on the island and by what external agencies the colonisation is effected.

The first germs of land-plants are brought by ocean-currents which carry seeds and fruits, drifting on the surface of the water, to the low-lying beach of emerging coral islands. Some of these seeds on arrival are still capable of living; they germinate and, provided the conditions are not too unfavourable, continue to grow and constitute the first plants of the island. It has long been known that only a comparatively small proportion of plants are capable of extending the area of their distribution by this means.

A comparison of island floras has shown that it is exclusively strand-plants—in the Malay Archipelago there are about 320 species—which have seeds and fruits possessing the necessary adaptations for this method of dispersal by ocean-currents, that is which are capable of floating for weeks or months on sea-water without losing the power of germination.

Among the agencies concerned in the colonisation of coral islands the second place may be ascribed to birds which use them as resting places or visit them in search of food. They serve in various ways to enrich island floras. Fruit-eating birds eject seeds which have passed uninjured through their intestine. In the process of cleaning and preening their plumage birds often rub off small fruits and seeds attached by hooks or other contrivances to their feathers or which are carried with earth or mud on their feet.

Numerous coral islands owe their first and most widely spread plants to ocean-currents and to birds. Spores and seeds of other plants, as extended observations have shown, are introduced by wind and occasionally by other agencies; these quickly fill up gaps in the vegetation, finding in the substratum already prepared by earlier arrivals, conditions favourable for germination and subsequent development.

In the case of Krakatau, Treub expected to find phenomena analogous to those already referred to as characteristic of the progress of colonisation of recently formed coral islands; he wrote: “Le littoral de l’ile se couvre de plantes à l’aide des graines amenées par les courants océaniques et par les oiseaux tout comme chez les iles de corail. Les éléments qui composent la flore de cette bande littorale remonteront petit-à-petit les versants de l’ile; cela est possible parceque la plupart de ces plantes, bien que préférant une station saline, croissent vigoureusement encore éloignées de la plage et à une assez grande altitude. Cependant, plus la bande végétale originaire de la plage remonte et plus sa marche se ralentira. Finalement ce sera presque uniquement par l’entremise des oiseaux que les parties les plus élevées de l’ile se peupleront de plantes. Une fois toute l’ile couverte d’un tapis végétal peu dense encore, le terrain sera peu à peu préparé a recevoir d’autres plantes dout les spores ou les graines sont amenées par le vent ou par d’autres causes.”

The actual method of plant introduction has, however, proceeded along altogether different lines. In June 1886, when the island was first visited by Treub, the pioneers of a new vegetation were seen from the shore to the peak and he was able to establish the important fact that the re-stocking of the beach and of the interior, including the slopes of the cone, had been effected simultaneously, though in different ways and for the most part by different plants. It was shown that blue-green Algae were the first colonists on the pumice and volcanic ash as also on the exposed blocks of rock in the ravines on the mountain slopes. Investigations made during subsequent expeditions demonstrated the association of Diatoms and Bacteria with the blue-green Algae. The dark green gelatinous layer with which these minute, self-sufficient, and doubtless wind-borne organisms covered the pumice and ash formed a favourable nidus for the germination of the spores of mosses and ferns and of the seeds of such phanerogams as are adapted by their small size and weight to dispersal by air-currents. An especially characteristic feature of the first stage of colonisation was the preponderance of ferns, which were represented by 11 species widely spread in the Indo-Malay Archipelago; only two of these, however, belong to the strand-flora of the islands.

In addition to cryptogams phanerogams were also met with on the island in 1886, though in comparison with ferns they were at first represented by a relatively small number of species and individuals. In the Drift-zone of the beach, Treub found seedlings of nine species of phanerogamous plants, the seeds of which had germinated on being washed up by the sea, also the fruits and seeds of seven other phanerogams which, like the former, belong to the strand vegetation characteristic of the Malay Archipelago. In the interior and on the slopes of Rakata, the number of phanerogams amounted to eight species, two of which were identical with those found on the beach. The remaining six species, four Compositae and two grasses, plants with light fruits—some of which were provided with special adaptations to wind-dispersal—were obviously, like the minute spores of the cryptogams, transported by air-currents from the neighbouring islands to the new land surface of Krakatau. Plants introduced by animals or man were not found on the uninhabited and barely accessible island.

The problem of the colonisation or re-stocking of a high volcanic island situated far from the mainland was thus solved in a remarkable manner by Treub's researches. It was demonstrated that the elements of the strand-flora played a very subordinate part in the composition of the new flora, a result entirely contrary to what one would expect from the analogy of coral islands where these elements are the first colonists. The flora of the interior of the island had developed not only independently of the strand-flora but also with much greater rapidity: the number of species was greater and in the case of certain ferns the number of plants was sufficiently large to constitute a characteristic feature in the general facies of the vegetation. A few phanerogams were first met with as isolated plants among the ferns both on the mountain and on the beach.

To follow the gradual changes in this new plant-world of the island, poor in species and brought together in so remarkable a manner, would clearly have been of the greatest interest. A thorough investigation of the group of islands planned by Treub for the following years had unfortunately to be given up, and it was not until ten years later, in March 1897, that the project was carried out, when Treub, Penzig, Raciborski, Boerlage, and Clautriau took part in a second exploration of Krakatau.

During the interval of ten and a half years between the first and second expeditions there had been a considerable increase in the number of species in both coast and inland floras. In 1897 the total number of species found on Krakatau and on the other islands visited by the expedition, Verlaten and Lang islands, which in 1886 were entirely destitute of vegetation, amounted to 62 species of vascular plants, including 50 phanerogams and 12 vascular cryptogams, in addition to the seeds and fruits of 26 phanerogamous plants washed up on the beach. The assemblage of plants had become denser and the ground was in places completely covered; the development of characteristic plant-associations (formations) had begun. On all three islands the Pes-caprae formation or association formed a dominant feature on the beach. Mangrove plants were unrepresented and the first sign of a strand-forest was noticed only on Verlaten island.

Further inland the vegetation constituted a kind of grass-steppe characterised by grasses, occasionally reaching the height of a man, which in several places formed a thick jungle. Lower grasses grew on the hills and ridges in association with numerous ferns and sparse phanerogams. As in 1886 ferns largely predominated on the rock surfaces. Shrubs were poorly represented and trees were very rare.

Of the 53 phanerogams found in 1897, Penzig estimates that 32 species (60·39%) had reached the islands by ocean-currents, 17 species (32·07%) by wind-agency, and only 4 (7·54%) had been transported by fruit-eating animals or by man.

Part 2

In 1905 another visit was paid to Krakatau, in which Th. Valeton, M. Golenkin and other botanists took part. The results of this expedition have not been published.

During my residence at Buitenzorg I made application, in company

with C. A. Backer, the author of a comprehensive “Flora of Batavia” which is now in the press, to Professor Treub to organise another expedition for the investigation of the Krakatau flora. As the result of his kind co-operation the authorities placed at our disposal a small coasting steamer which was then on the point of visiting certain places on the coast of the Sunda Strait to relieve the lighthouse keepers. The excursion was to last four days and the departure was fixed for April 24th. Unfortunately Professor Treub was prevented by illness from accompanying us, but we were joined by two botanists who happened to be studying in the Buitenzorg botanic garden, Dr A. A. Pulle from Holland and Prof. D. H. Campbell of California.

The plants collected by C. A. Backer and Dr A. A. Pulle in the course of our Krakatau excursion, on the island and at different localities on the coasts, were determined by the former, who was kind enough to undertake the revision and to some extent the identification of the vascular plants collected by myself. The list of phanerogams and vascular cryptogams which we collected, communicated to me by C. A. Backer, will appear either in Verslag van’s Lands Plantentuin te Buitenzorg or in the Mededeelingen uit’s Lands Plantentuin te Buitenzorg. As a matter of convenience I have arranged the plants in the following lists according to families, including the names of some species of widely distributed and well known plants of which, though no specimens were collected, records were made in my notes written on the spot.

Since the appearance of the German edition of this account Dr Pulle and Prof. Campbell have published some of the results of their own observations, the former in a detailed abstract of this work and the latter in a paper on the distribution of liverworts.

In beautiful weather on the morning of April 24th, 1906, the “Snip” (Snipe) left the harbour of Tandjong Priok to steer a western course among the numerous small coral islands scattered along the north-west coast of Java. Our first objective was the island of Edam, barely 12 kilometres distant, which like Onrust, Leyden and other small islands outside the harbour of Batavia, was formerly inhabited. Today the European keepers of the large lighthouse and their Javan servants are the only inhabitants. The inhospitable islands with their ruined houses and grass-grown streets are the home of a dangerous malaria. Swarms of gnats attack the inhabitants at night and are troublesome even in the daytime as one wanders through the thickets. The strong smell from decaying plants and marine animals, the moisture-laden air and almost intolerable heat bear eloquent testimony, even after a short visit, to the injurious consequences which are bound to follow a longer residence on one of these islands. The lighthouse keepers, in spite of a comparatively high scale of payment, remain a short time only and return with their families after 1—3 months service on a long furlough to the healthier climate of Batavia. The island is encircled by surf; at the narrow entrance our boat bumped against the small stone pier which has been built on the coral reef for the convenience of landing. In the course of the repeated journeys of the boat necessary to land provisions for the small number of inhabitants, also the petroleum for the lighthouse lamp, and the post-bags and monthly wages, we had time to explore the island. After traversing streets overgrown with tall grass, and passing through a small vegetable garden and a plantation of coconut palms to a waste piece of formerly cultivated land, we reached the interior and the opposite beach, where broad strips of the original vegetation still remain.

On the way we found several specimens of a large arborescent euphorbiaceous plant, Phyllanthus Emblica, draped with tangled skeins and thick coils of yellowish green and brown threads. All the branches and twigs are covered by a dense network of similar threads and the same felted mass hangs from the grasses and herbaceous plants growing under the trees. These long threads are the stems of a climbing parasitic species, Cassytha filiformis, which bears a striking resemblance in habit to our native species of Cuscuta, though it is a member of the family Lauraceae, which has no close affinity with the Convolvulaceae to which Cuscuta belongs. The vegetative system, like that of Cuscuta, consists of branched climbing shoots bearing adventitious roots modified as haustorial organs which attach themselves to the tissues of the hosts. The true roots have disappeared and the leaves are reduced to small inconspicuous and functionless scales. The reproductive shoots, on the other hand, both flowers and fruits, are abundantly developed and occur in large spherical or elongated masses. The white fruits are in marked contrast to the tangled felt of host and parasite; birds eagerly eat them and by ejecting the seeds contribute in an important degree to the dispersal of this interesting member of the strand-flora, which is not as yet so completely adapted to a parasitic life as Cuscuta. It has the power of independent assimilation and grows impartially on nearly all the plants of the strand vegetation. The interior of the island is occupied by a thicket of various trees and shrubs. With Phyllanthus Emblica and Phyllanthus simplex occurs Acalyphe indica, another representative of the family Euphorbiaceae which is rich in halophilous species; also the leguminous plants, Bauhinia Blancoi and Leucaena glauca, the young fruits and ripe seeds of which are eaten by natives in the Archipelago as a relish with their meals of rice. The ground is covered with herbaceous plants, bushes and shrubs, principally of the families Gramineae, Cyperaceae, Compositae, Labiatae, and Leguminosae. Our guide warned us to be careful in entering the bush, as in addition to the large but harmless snake, Python reticularis, which reaches a length of 3 to 4 metres, some smaller poisonous species are also met with.

The south coast of the island is flat and sandy. A broad belt is covered with a low and almost shrubless vegetation, of which the two characteristic plants are Spinifex squarrosus and Ipomaea Pes-caprae. Each of these is admirably adapted to a strand habitat. Spinifex squarrosus is a stiff bluish glistening grass with tufts of rounded and sharply pointed leaves bound together by tough runners hidden in the sand. The low form of growth, the anchoring of the stems in the loose sand by deep roots, are adaptations to a habitat exposed to frequent and strong winds.

The conditions, which are unfavourable for vegetative development, have been utilised in a remarkable manner by Spinifex for the dispersal of its fruits. The fruiting shoots are very large and completely spherical. The spikelets are crowded in the centre of a ball as large as a man’s head at the base of long stiff axes which spread out on all sides like bristles (Pl. VII., fig. 10). The ripe fruiting shoots fall off and are rolled as light balls over the sand until they attach themselves to other plants or become the sport of the waves. Some of these small fruits are detached during the process, while others remain fixed to the shoot for a longer period and with it are carried by the wind over wide stretches of the beach or transported by currents to other islands. Single shrubs and taller herbaceous plants appear above the groups of Spinifex squarrosus, Ipomaea Pes-caprae, and Ipomaea Pes-tigridis; of these the most striking are the abundant and handsome plants of Tacca pinnatifida with its two to four large umbrella-like leaves and strong reproductive shoots.

On the north coast trees and shrubs extend to the water‘s edge or even into the water. We found in Edam a mangrove belt poor in species, an association not often met with on small coral islands. It consists chiefly of species of Rhizophoraceae, Rhizophora conjugata, Brugiera gymnorhiza, Brugiera caryophylloides, with two members of the Lythraceae, Sonneratia alba and Pemphis acidula.

A considerable area of the interior, formerly under cultivation, is now covered with grasses, especially with Imperata arundinacea, which exceeds the height of a man. By the sides of the paths we found several specimens of the common blue-flowered Javan verbenaceous species Stachytarpheta indica and Lantana Camara, the inflorescences of which glow with different shades of yellow and red; also numerous Compositae which, like Bidens pilosus, Vernonia cinerea, and Wedelia glabrata, occur in all the warmer regions of the world, or, like Tridax procumbens and particularly Synedrella nodiflora, have spread from the New World over the tropics of the Old. The amount of material collected during our excursion, which lasted barely two hours, was remarkable. It consisted of 75 phanerogams and 2 vascular cryptogams. On the coral reef I was able to collect 12 different green algae, the commonest being species of Caulerpa, Udotea, and Halimeda; also some red and brown sea-weeds.

As the composition of the flora on the neighbouring islands is probably similar to that of Edam and as our collection is of interest from the point of view of comparison with the floras of other coral islands such as Schimper and Guppy have described, the list of the species obtained on Edam is appended:

| Angiospermae:

Fam. Compositae: | Bidens pilosus L.

†Eclipta alba Hassk.

Synedrella nodiflora Gaertn.

Tridax procumbens L.

Vernonia cinerea (L.) Less.

Wedelia glabrata B. et H.

Fam. Goodeniaceae: | †Scaevola Koenigii Vahl.

Fam. Rubiaceae: | †Guettarda speciosa L.

†Morinda citrifolia L.

Oldenlandia umbellata L.

Fam. Labiatae: | *Anisomeles albiflora Miq.

Leucas linifolia (Roth) Spreng.

Ocimum basilicum L.

Fam. Verbenaceae: | †Clerodendron inerme Gaertner

Lantana Camara L.

†Premna foetida Reinw.

Stachytarpheta indica Vahl.

†Vitex Negundo L.

Fam. Borraginaceae: | †Cordia subcordata Lam.

Fam. Convolvulaceae: | Calonyction asperum Chois.

†Ipomaea Pes-caprae Sw. [= I. biloba]

Ipomaea Pes-tigridis L.

Fam. Asclepiadaceae: | †Hoya spec.

Fam. Myrtaeeae: | *Eugenia Jambolana Lam. (?)

Fam. Rhizophoraeeae: | †Brugiera caryophylloides Bl.

†Brugiera gymnorhiza Lam.

†Rhizophora conjugata L.

Fam. Lythraceae: | †Pemphis acidula Forst.

†Sonneratia alba Smith

Fam. Passifloraceae: | *Passiflora foetida L.

Fam. Sterculiaceae: | Sterculia foetida L.

Fam. Malvaceae: | †Thespesia populnea Corr.

Fam. Vitaceae: | *Vitis trifolia L.

Fam. Rhamnaceae: | †Colubrina asiatica Brongn.

Sageretia oppositifolia Brongn.

†Zizyphus Iujuba Lam.

Fam. Sapindaceae: | *Allophyllus Cobbe Bl.

Schleichera trijuga Willd.

Fam. Anacardiaceae: | Buchanania florida Schauer

Fam. Euphorbiaceae: | *Acalyphe indica L.

†Euphorbia Atoto Forst.

Phyllanthus Emblica L.

Phyllanthus simplex Mull. Arg.

Ricinus communis L.

Fam. Meliaceae: | †Carapa moluccensis Lam.

Fam. Leguminosae: | †Abrus precatorius L.

Bauhinia Blancoi Baker

†Canavalia obtusifolia D.C.

Crotolaria Saltiana Andr.

†Desmodium triflorum D.C.

Indigofera tinctoria L.

Leucaena glauca Benth.

Zornia diphylla Pers.

Fam. Lauraceae: | †Cassytha filiformis L.

†Hernandia peltata Meisn.

Fam. Portulacaceae: | *Portulacca australis Endl.

+Portulacca oleracea L.

Fam. Aizoaceae: | †Sesuvium portulacastrum Willd.

Fam. Nyctaginaceae: | †Boerhavia repanda Willd.

Fam. Amarantaceae: | *Aerua lanata (L.) Juss.

†Achyranthes aspera Lam.

Fam. Taccaceae: | †Tacca pinnatifida Forst.

Fam. Palmae: | †Cocos nucifera L.

Fam. Cyperaceae: | †Cyperus pennatus Lam.

Cyperus hyalinus Vahl.

Fimbristylis spathacea Roth

Fam. Gramineae: | Andropogon contortus L.

Eleusine aegyptiaca Desv.

Eragrostis tenella R. et Sch.

Imperata arundinacea Cyr.

Paspalum distichum L.

Paspalum sanguinale Lamk.

†Spinifex squarrosus L.

†Thuarea sarmentosa Pers.

†Zoysia pungens Willd.

| Pteridophyta:

Fam. Polypodiaceae: | †Polypodium quercifolium L.

Polypodium acrostichoides Forst.

Drymoglossum spec.

Not less than 36 of the plants (indicated in the list by †) are included in Schimper’s list of the Indo-Malayan strand-flora as typical halophytes, and 19 additional species (distinguished by *) belong to genera which include characteristic strand species. In the case of the majority of these plants there is no doubt that the seeds and fruits are easily distributed by ocean-currents. A smaller number, in view of the comparatively short distance between Edam and Java, probably owe their introduction also to wind-agency. These are: Eclipta alba, Wedelia glabrata, Cyperus hyalinus, Fimbristylis spathacea, Polypodium quercifolium, or possibly introduced by birds: Scaevola Koenigii, Morinda citrifolia, Clerodendron inerme, Premna foetida, Vitex Negundo, Allophyllus Cobbe, Cassytha filiformis.