After leaving the University Campus the first part of the route is through residence and business areas of the city. The steep slopes on the left below the University are covered by *Leucaena scrub. The gradual climb, after emerging from the valley and turning to the left on the main arterial highway, is over a relatively recent lava flow which fills the saddle between the conspicuous Diamond Head buff cone on the right and the steep ridges of the main Koolau volcanic massif. Just beyond this, at the mouths of the first two gulches, is a remnant of an old elevated coral reef which fringed much of the south side of Oahu at a higher stand of the sea (or a lower stand of the island). This is covered by residences. The bottoms of all the valleys that reach the sea along this coast are filled by alluvium washed down from the volcanic slopes above. The mouths of most of them have accumulated beach deposits of coral sand and locally slightly raised reefs are exposed. This relatively flat land has been completely converted to suburban housing developments except for the part to the right of the highway for a mile or so, which is landscaped as a golf course. The double highway in this area has a strip in the center planted to *Jasminum multiflorum and *Lantana sellowlanum and is largely lined on the sides by hedges of ornamental *Hibiscus and *Nerium. On the left, along the road between Wailupe and Niu valleys is a row of *Delonix regia (flamboyant).
The ornamental *Hibiscus hybrids that are such a characteristic feature of the built up parts of Hawaii are a tremendous assortment of cultivars formed by hybridizing various native Hawaiian Hibiscus species with the introduced *H. rosasinensis, *H. schizopetalus and a number of others that happen to be somewhat compatible. Many of them are monstrous double forms, but some are extremely beautiful. The flowers are open only one day before fading. Many thousand of these cultivars have been produced and it is not known how many are maintained or still exist in cultivation. They are all propagated vegetatively.
The highway passes the mouths of a series of deep valleys cut in the old lava leeward slopes of the Koolau Range. Patches of montane rain forest may be seen in the distance in the steep heads of these valleys. On the sides of the valleys, the lower slopes are covered with *Prosopis forest, the middle slopes with *Leucaena and *Schinus terebinthifolius scrub, the higher slopes and ridges with irregular *Lantana scrub and grass. The fore slopes and spurs on the seaward ends of the ridges tend to be grassy with Heteropogon and various introduced grasses and weeds, *Opuntia and patches of *Lantana and other shrubs.
*Prosopis dominates the lower parts and the flat land wherever it is not built up into residential developments. Some of the ridges, especially near Kuliouou Valley, are badly eroded. Egler (1947) published an excellent description of the vegetation of this arid slope of southeast Oahu. The area exemplifies very well the rainshadows found on leeward slopes of the islands.
Where the road swings to the right, it follows a barrier beach ridge that separates the extensive Kuapa Pond, an old Hawaiian fish pond, from Maunalua Bay. In the bay, to the right, are extensive fringing coral reefs and very shallow water. The pond was formerly surrounded by extensive flats dominated by *Batis maritime and was an important habitat for water and shore birds. Now, as will be seen, this has been sacrificed to a marina and yacht harbor. Ahead may be seen one of the striking scenic profiles of Oahu, with the steep tuff cone, Koko Crater, on the left and the long sweep of Koko Head to the right. The forces of "Progress" have not been able, as yet, to destroy this view completely.
As these cones are approached more closely it will be seen that erosion has made its inroads, especially on Koko Head, the slopes of which are almost bare and deeply fluted by radiating ravines. Grazing is not now permitted here, but the effects of former grazing and fires are very difficult to heal over in such a dry environment. Koko Crater is covered by thin grass, with *Prosopis forest around the base and a a few spots of *Schinus near the top.
At the top of the saddle between the two cones a side road bends sharply back to the right and an exquisite small bay is spread out below, occupying the crater of still another, but lower, tuff cone, open on the southeast side toward the sea. The inner slopes of the crater are partly bare, partly, especially on the north side, wooded with *Prosopis with a loose understory of *Leucaena. Around the bay, on the slope of Koko Head, are patches of conspicuously windsheared *Prosopis, interspersed with patches of grass and erosion scars. The *Prosopis on the flat ground back of the parking lot forms a dense forest, but the undergrowth is cleared out for picnic table sites.
The walk down to the beach is cut in bluffs of bedded tuff, a poorly consolidated pyroclastic volcanic rock laid down by the explosive eruptions which occurred during the last volcanic episode on Oahu. Along the path is a poor weedy vegetation of*Chloris inflate, *Tricholaena rosea, *Alysicarpus vaginalis *Passiflora foetida, *Waltheria indica, *Atriplex semibaccata, *Leucaena leucocephala, Sida cf. fallax, and Boerhavia repens. At the base, back of the beach flat, is a *Leucaena thicket, and around a small pavilion are planted *Casuarina equisetifolia, Cocos nucifera, *Ficus microcarpa, *Malvaviscus arboreus, *Canna sp., *Polyscias guilfoylei and *Plumeria rubra. A thin lawn of *Cynodon dactylon covers the sand flat back of the beach.
The beach here is a grayish or greenish sand largely made up of olivine crystals, which sparkle brilliantly in the sunlight. On the very low beach ridge and sand flat behind it that stretch in a crescent around the bay to the right, a characteristic weed vegetation can be seen, made up of at least the following species: *Chenopodium murale, *Cenchrus echinatus, *Eleusine indica, *Chloris inflate, Ipomoea indica, Argemone glauca, *Reichardia tingitana, *Sonchus oleraceus, *Setaria verticillata, *Dactyloctenium aegyptium, *Malva parviflora, *Merremia aegyptia, *Verbesina encelioides, Tribulus cistoides, *Batis maritime, *Ocimum gratissimum, and Sida cf. fallax. The Hawaiian Sida species have usually been referred to Sida fallax, some to S. cordifolia. Recently Professor St. John has found that an amazing complex series of local populations exists, based principally on fruit characters, but his taxonomic disposition of these has not yet been published.
At the end of the beach to the right is a patch of Thespesia populnea and Hibiscus tiliaceus, rather dense, low and depressed, probably from exposure to the wind and spray. Some of the Hibiscus shows an unusual tendency to have the leaves green, rather than gray tomentose beneath.
A trail climbs the rather abrupt slope through this vegetation. The first 50 m are rather difficult to climb. However, this is the only part of the trip that may give trouble. This slope is eroded and in places very sparsely vegetated. Patches of prickly scrub of *Prosopis, *Acacia farnesiana, *Lantana camera, and *Leucaena form a mosaic with lower vegetation of Heteropogon contortus, Lipochaeta integrifolia, Jacquemontla sandwicensis, Sida cf. fallax, Eragrostis variabilis, *Portulaca oleracea, *Stachys arvensis, Ipomaea cairica, *Ocimum ~ratissimum, *Waltheria indica, *Reichardia tingitana, *Emilia javanica, *Ageratum conyzoides, *Cassia leschenaultiana, and perhaps other dryland native species and weeds. The trail continues through this mosaic, which soon becomes preponderantly *Acacia farnesiana (klu), to the top of the outer slope of the tuff cone.
On the top is a flattish gently sloping area almost devoid of vegetation, appropriately described as a miniature desert. Doubtless originally denuded by grazing, it has been kept this way by continuing wind and water erosion, exposing the indurated tuff, and providing an inhospitable habitat, indeed, for most plants. To the right is a low windsheared forest or scrub of *Prosopis pallida. On the bare ground underfoot are occasional single plants or small tufts or patches of a number of hardy species, mostly in slight irregularities or pits in the ground. Of these the most interesting is Panicum faurei, one of a small group of native species of Panicum found mostly in exposed or at least open dry places. It is prostrate and well adapted to this bare windy situation. The other native species here are Lipochaeta integrifolia, an interesting succulent, characteristic of saline places, Heteropogon contortus, Heliotropium curassavicum, possibly but not certainly native, and Fimbristylis cymosa, a sedge found under many names in saline places in most tropical countries. *Chloris, *Dactyloctenium, *Digitaria, *Atriplex, *Waltheria, *Passiflora, *Sonchus, and *Reichardia are also here, mostly in very depauperate forms.
This gentle slope, as the route crosses it to the south, changes from a smooth to a rubbly, then to a grooved or slightly gullied surface, with the plants more and more confined to small pits.
A shallow depression, really an old crater occupies a considerable area. The low ridge separating this from the slope toward Hanauma Bay, clearly shows what has happened to produce the desert that surrounds it. A layer of fine ash soil, held by a sod of *Chloris and *Cynodon, with some ether plants, can be seen on the top of the low ridge, extending into the crater. Its outer edges are clearly being cut back by the wind, but are held by the grass and *Prosopis roots. There seems little doubt that a soil of this character once covered all but the steepest parts of Koko Head.
The floor of this small crater is open but the inner slopes are covered with a low *Prosopis scrub, the upper surface windsheared down almost to the level of the crater rim. The floor is of fine silt covered by grass and other herbs. The lowest part is a solid sod of one of the most interesting Hawaiian ferns, Marsilea villosa. This is invaded substantially by weeds, especially *Xanthium cf. strumarium, *Chloris inflate, *Setaria verticillata, *Commelina benghalensis, *Reichardia' *Merremia aegyptia, *Malva parviflora, #Echinochloa colonum, *Phaseolus lathyroides, *Emilia javanica, *Waltheria, *Sonchus oleraceus, Jacquemontia, *Digitaria (Tricachne) insularis, *Cynodon, *Passiflora, *Ageratum, #Solanum nigrum, and *Malvastrum coromandelianum. After periods of heavy rainfall, such as kona storms, this area is submerged under a meter or more of water for considerable periods, which may be the reason it has not been occupied by woody plants. From the crater, looking west, one can see striking silhouettes of windsheared *Prosopis on the horizon.
East of this crater is an almost bare slope of eroded tuff, with scattered tufts of another interesting native plant, Schiedea globosa, belonging to an endemic Hawaiian genus of somewhat shrubby Caryophyllaceae, the species restricted to the area covered by the present excursion, in southeastern Oahu. This Koko Head population of it, which seems to be increasing, is fairly uniform and shows strongly the characteristics of a halophytic succulent. Another population, to be seen later, contrasts with it in several respects.
Over the top of this ridge the seaward slope is also severely eroded and almost as bare of vegetation. Small patches of many of the same species listed above for the eroded flats are found here, mostly in the small gullies and depressions. Lower down, plants become fewer and the rock is fantastically shaped by wind erosion. Downward, the last straggling plants are *Chloris, *Dactyloctenium, *Portulaca and *Sonchus, with a patch of Panicum faurei on a small ash terrace, and, most remarkable of all, a few tiny plants of another Hawaiian endemic, Nama sandwicensis, in rock crevices. Elsewhere, it grows only on sand dunes, and most known localities for it has been destroyed by the development of beach homes and military installations. The lower 2530 m of this slope has no vegetation. It is wet by spray from the breaking waves beneath and the sea water dries leaving thin deposits or crusts of salt.
The return trip is made along the slope above Hanauma Bay, where, in the most exposed parts, are found many of the same species listed above for the eroded areas, but in addition *Desmodium triflorum, *Euphorbia hirta, *Stachytarpheta jamaicensis and the endemic Panicum torridum, a more luxuriant and much more hairy plant than the related P. faurei, also found here. On a more sheltered aspect of this slope the vegetation includes many of the same species' but is much more luxuriant, and with such additional species as Vigna marina (normally a beach plant), Heteropogon contortus and Boerhavia repens. The latter is very rare, but is said to have been abundant here 5 years ago. Extreme caution is urged in exploring this slope. It is a "dip slope" of crumbly tuff, and if a person misses his footing there is nothing to stop him but the rocks at the foot of the cliff below.
The return route from here crosses the eroded flats described above, to the edge of another, somewhat deeper, crater, filled with dense *Prosopis forest. Along the north edge of this may be seen *Asystasia gangetica and *Schinus terebinthifolius,and on the steep slope above, a patch growth of Heteropogon and windsheared clumps of *Prosopis. This slope is a short but stiff climb. From the top, on the main ridge of Koko Head, there is a magnificent view of the coral reefs in Hanauma Bay, of the fringing reef in Maunalua Bay on the opposite side of Koko Crater, and of the serrate crest of the east end of the Koolau Range. From here it is a,' easy walk down the road to the parking lot. *Desmanthus virgatus, *Crotalaria mucronata and *Euphorbia prostrate are additional weeds that may be seen along the road.
The highway on from Hanauma Bay is cut through bedded tuff and cinders thrown out of a small cinder cone called Kahauloa, to the left of the road. This tuff is very interesting because it contains a mixture of coral pebbles, showing that the explosion came up through an old coral reef or beach deposit. It is vegetated principally by *Prosopis forest and the curious Scaevola taccada (naupaka kai), a widespread IndoPacific beach species belonging to the principally Australian family Goodeniaceae. Several upland species of this genus will be seen on later excursions into the mountains.
After passing Kahauloa Crater the road skirts the base of Koko Crater, with low sea cliffs on the right, and passes the famous Blowhole. this is a place where waves thunder into a cave worn in the tuff cliffs and force spray through a small hole high into the air. It has, however, been badly disfigured by construction designed to enable the public to view it in complete comfort.
From here the road follows a wide beach flat for some distance. A brief stop will be made to examine Heliotropium anomalum and Ipomaea pescaprae growing on the sand. Beyond here, a formerly very interesting dry land area has been destroyed by an enormous residence development. Here, by accident, a single tree of the endemic Erythrina sandwicensis (wiliwili) and the very interesting and important endemic cotton, Gossypium tomentosum have been left along the road. If they still survive by the time of the excursion, stops may be made to see them.
The road then climbs up through *Prosopis forest. The cliffs on the left are covered principally by Heteropogon contortus (pili). Abutilon incanum, with a curious distribution, Hawaii and the deserts of southwestern U. S., may be seen just before the road reaches the pass behind Makapuu Head. From the pass and the grade beyond, there is a good view of two small islands, Kaohikaipu and Manana, both extinct tuff cones, and both protected as seabird refuges.
A stop will be made part way down the grade below the pass and the party will walk the short distance down to the park on the shore below, examining the plants on the cliffs along the road. Great care must be taken by everyone here, as auto traffic may be heavy and the roadsides are narrow.
A patch of the endemic Canavalia galeata is seen below the road to the right. Careful study of this species has revealed an interesting series of local variations, possibly of importance in elucidating patterns of evolution in this widespread genus. Other native species found on these cliffs and talus are Scaevola taccada, Sida cf. fallax, Panicum torridum, P. faurei, Doryopteris decora, Argemone glauca, Boerhavia repens, Lipochaeta integrifolia and Schiedea globosa. This population of the latter species contrasts with that seen earlier on Koko Head, in its extreme variability, especially in leaf shape, from linear to ovate, and in its much thinner texture and dull leaf surface. The two populations have been described as separate varieties. Many weeds are also seen here, most of them the same as listed for Koko Head. *Cucumis dipsaceus, a spiny cucumber, is an addition to the list.
Below, the flats back of the beach are partly sandy and partly of lava boulders. The general vegetation is an irregular low scrub of Scaevola taccada, with Santalum ellipticum, very depressed *Prosopis, locally some *Leucaena leucocephala and, near the beach, Lycium carolinianum, a dwarf strand shrub found on both coasts of southern North America, in the southeastern Polynesian islands, and in Hawaii. Many herbs and dwarf shrubs occur in the openings in this scrub, such as *Eragrostis tenella, *Cenchrus echinatus, *Digitaria henry), *Digitaria (Tricachne) insularis, Sporobolus virginicus, Panicum faurei, P. torrldum, *Dactyloctenium aegyptium, Fimbristylis cymosa, *Atriplex semibaccata, Boerhavia repens, Cocculus ferrandianus, *Coronopus didymus, Tribulus cistoides, Euphorbia degeneri, *Euphorbia prostrate, Sida cf. fallax, Anagallis arvensis, Ipomoea pescaprae ssp. brasillensis, I. indica, *I. cairica, *Merremia aegyptia, Cuscuta sandwichiana, Jacquemontia sandwicensis, Hellotropium anomalum, *Stachys arvensis, Asystasia gangetica, *Verbesina encelioides, *Emilia javanica, *Reichardia tingitana, and *Sonchus oleraccus.
Although it will be seen that many native species still persist, there has been a great degree of alteration of the vegetation and replacement of native plants by exotics.
Depending on the time still available, the return to Honolulu will either be by the same route, or by one of the more scenic highways over and through the mountains.
