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Manoa Valley, in which the University of Hawaii is situated, is typical in many ways of the land forms produced by erosion in older Hawaiian basaltic lavas. The Ushaped cross section and cirquelike head, the "amphitheaterheaded" valley (Stearns 1946, p. 7), are produced, not by glaciation as would be suspected in temperate mountains, but by stream erosion in basalt under a particular range of conditions of slope, bedding and high rainfall. Some of the world's most spectacular scenery is found in such valleys and it may be seen to good advantage from the Manoa Cliff Trail. This trail follows the upper edges of the cliffs around a portion of the west wall of Manoa Valley, just above the 400 m contour, from above the hills called Puu Ulakaa (Round Top), 330 m and back of Puu Kakea, 485 m, to Pauoa Flats, just behind Puu Ohia (Tantalus), 650 m, where it joins the the Pauoa and Tantalus trails. Although the areas traversed by these trails have been profoundly altered by longcontinued human activity, they present the most readily accessible opportunity for the visitor to see several of the important Hawaiian vegetation types and many native Hawaiian rainforest plants.
Leaving the University Campus, the excursion route follows Wilder Avenue, lined with *Delonix regia (royal poinciana or flamboyant). The oncefamous nightblooming cereus hedge (*Cereus undatus), cut away during the warhysteria following the Pearl Harbor attack and not very successfully reestablished, surround the Punahou School campus, on the right. Here also is a fine row of *Roystonea regia (royal palm). At Makiki Street the route turns "mauka" (towards the mountains), and soon starts up Round Top Drive, making a series of switchbacks up the bold face of Round Top. This hill is composed of beds of a very weakly consolidated tuff or cinders commonly called "black sand," widely used for growing orchids and other plants, also for making concrete blocks. A quarry or pit where this is exposed may be seen on the right part way up. This slope is covered by *Leucaena leucocephala (koa haole) scrub where residences do not cover it. Along the upper portions of this drive the vegetation is composed of thickets of Hibiscus tiliaceus (hau) and a great display of exotic plants, both weeds and escapes from cultivation. Planted trees of many sorts are seen along the drive after the main climb, especially around the fine estates established in this cool upland.
The entrance to the Manoa Cliff Trail follows a sloping driveway with, on the left, a row of #Cordyline fruticosa (ti) and *Psidium cattleianum (strawberry guava or waiwi) and *Eugenia jambos (rose apple) on the right. *Ligularia kaempferi is planted along the side of the entrance to the trail. As the trail passes through a yard and onto the trail, proper, #Aleurites moluccana (kukui) and Acacia koa (koa) arch overhead. Just to the left, a strangling fig (*Ficus sp.) demonstrates its habit on a koa tree above the trail. A large grass, *Setaria palmifolia, is so abundant along the trail as to form an obstruction where it is not kept cleared. Its plicate leaves are very characteristic. Along the trail here, also, are such weeds as *Ageratum houstonianum, *Emilia javanica, *Ruellia graecizans, *Passiflora edulis, and *Stachytarpheta dichotoma. About 100 m along the trail, on the right, is the first specimen of Freycinetia arborea (ie de), a climbing member of the Pandanaceae, found generally in the moist to wet Hawaiian forests, and with relatives throughout the IndoPacific islands. It is interesting because of its fleshy, salmoncolored floral bracts which seem to be adaptations to pollination by rats and probably fruit bats. No one is quite sure, however, how the Hawaiian species was pollinated before rats were brought to the islands by the Polynesians. *Persea americana (avocado) grows overhead here and two trees of *Elaeocarpus sp. are planted to the left of the trail. Koa and kukui are common, overhanging the trail.
About 100 m farther on is an extensive grove of a rhizomatous bamboo, and just beyond, a patch of #Aleurites moluccana (kukui) forest on the right. *Lantana camera and *Rubus rosaefolius are found along the trail, the latter with bright red, thimbleshaped edible fruits. Banana plants, with enormous leaves, are on the right, and above the first bend in the trail are small tree ferns (Cibotium splendens). *Commelina diffuse occupies a small flat place. Then on the right *Psidium guajava (guava) is seen, and P. cattleianum (strawberry guava) on the left. The latter becomes abundant after a short distance. On the left, just before the second bend in the trail, is a tangle of Gleichenia linearis (uluhe) with shrubs of Scaevola gaudichaudiana (naupaka). At this bend, the trail forks. The left fork should be followed, through strawberry guava brush. The smooth purple flowered verbena is *Stachytarpheta urticifolia. On grassy slopes, Paspalum orbiculare, *Sacciolepis indica, *Setaria geniculata, and *Cassia leschenaultiana are common. The vegetation here for some distance is a thicket of strawberry guava with emergent Acacia koa trees. Beyond this is a patch of #Cordyline fruticosa, with several large guava trees above the trail and kukui below on the right. From here on the trail is frequently lined with a rank growth of *Eupatorium riparium, a weedy species that has occupied open banks, roadsides, and cliffs, spreading rapidly from a relatively limited occurrence noted in Hawaii above Hilo about 30 years ago.
At the sharp left turn, the first small Metrosideros collina (ohia lehua) appear, forming an irregular scrub with one of the shrubby native Euphorbia species, probably E. multiformis (akoko). From here on native species of plants become frequent. A native Bidens and Phyllanthus sandwicensis occur on the banks above the trail. The general vegetation is a scrubby wood of Metrosideros and Acacia koa. Just beyond a large koa tree which hangs over the road is a tree of Bobea elatior, endemic genus of Rubiaceae, on the right, and a thicket of Psychotria (Straussia) kaduana. Around a small bend in the trail, under an #Aleurites tree, are several plants of one of the native lobeliads, Cyanea angustifolia mostly below the trail. A bit farther on is a slender shrub of Coprosma longifolia (pilo). Eragrostis variabilis begins to appear on the bank to the left. Fifty meters beyond the bend, among slender Metrosideros, is Scaevola gaudichaudiana. The Metrosideros here begins to show some of its famous variation. Beyond a large rock outcrop are several trees of Hibiscus arnottianus, the native white Hibiscus which has entered into many of the ornamental hybrids. Under the Hibiscus, below the trail, is another lobeliad, the strange looking Cyanea grimesiana. Beyond this are several neat compact narrowleafed bushes of Coprosma foliosa (pilo). Selaginella menziesii is common on rocks above the trail, and occasional purple ground orchids, *Spathoglottis plicate may be seen.
A little farther on is an open koa stand with Freycinetia arborea (ie ie) vines, and a ground cover of *Setaria palmifolia. This extends for some distance, with guava scrub and occasional Bobea elatior (ahakea) trees below the trail, and under the koa, occasional Scaevola, Psychotria, Metrosideros, and *Psidium. The pale frosty green trees below are *Aleurites (kukui).
Around the sharp bend to the left in the trail, there is mixed scrub on steep clifflike slopes, with a large lehua tree below the trail. On rocks are Eragrostis variabilis, Sphenomeris chinensis, *Blechnum occidentale, Psilotum nudum and Bidens sp. In open grassy spots, Lycopodium cernum may he seen, like a diminutive Araucaria. Around an S bend are shrubs of Xylosma hawaiiensis on the right, and a well formed tree of Eugenia sandwicensis (ohia ai).
Then comes a koa forest with guava, *Lantana camera, *Psidium cattleianum, and Freycinetia forming the shrub layer. Up the slope is a tangle of Gleichenia linearis (uluhe) and scattered Scaevola gaudichaudiana. Occasional plants of a white flowered form of *Lantana camera. Metrosideros (lehua) is occasional. A little farther on, in a small opening with *Setaria palmifolia are vines of *Passiflora edulis (lilikoi, or passion fruit), with edible purple fruits. From here is a view of the light colored patches of #Aleurites forest below. On an S curve to right and left is open koa forest with large trees, Freycinetia vines, and a ground cover of *Setaria and *Rubus rosaefolius. After a couple of hundred meters, to right, the trail turns sharply to the left. Just before this, on a lehua tree leaning over the trail are a clump of epiphytic Nephrolepis sp. and wisps of a grasslike fern, Vittaria rigida. After a short distance through koa forest with guava and kukui, there is a bamboo grove above the trail, then a patch of lehua with Scaevola and Psychotria. On a large lehua tree below the trail are several epiphytes including Ophioglossum pendulum var. falcatum and Psilotum nudum. Then comes more koa. Below the trail are several Pouteria sandwicensis trees with coppery young growth, also a small Antidesma platyphylla tree. A little way on is a patch of a strange looking fern, Athyrium proliferum, a tree of Perrottetia, then large guava trees and Cortyline fruticosa (ti). Then comes an Antidesma tree with Dioscorea bulbifera, a yam with aerial tubers, and small banana plants below the trail. They probably belong to one of the varieties brought by the ancient Hawaiians and now found only in small colonies in the wet mountain forests. A few meters on, there is below the trail a tree of Elaeocarpus bifidus, a tree that is found only on Kauai and Oahu. On a curve to the left the trail goes under a lehua tree and into a patch of forest with lehua, koa, Elaeocarpus, Coprosma, Ilex anomala, and Perrottetia hanging over the trail, then guava forest. On the Elaeocarpus is the parasitic Korthalsella complanata. After this is a curve from which the panorama of upper Manoa Valley, and, if the weather is right, of Puu Konahuanui, second highest mountain on Oahu (950 m), may be viewed.
A scrub of Psychotria mariniana and farther on, a small Gouldia terminalis var. coriacea are on the right at the edge of the cliff . Here also are small trees of Diospyros ferrea var. sandwicensis (lama), Hawaiian representative of a widespread IndoPacific species of the Ebenaceae. Then there is an open cliff covered by #Cordyline, and, above the trail, a mixed scrub with Dubautia plantaginea, representative of a remarkable group of endemic Hawaiian Compositae. In a small clump of wood are Hibiscus arnottianus, Perrottetia sandwicensis, Acacia koa, and Pipturus albldus, then more #Cordyline on the cliff and Zingiber zerumbet on the trail. In the next clump of HibiscusMetrosideros wood, a noxious, foulsmelling vine *Paederia foetida (Maile pilau) is established. Then come guava thickets with some native plants, including Gouldia terminalis, Heydyotis acuminate, Perrottetia, Hibiscus and the scarlet flowered leguminous vine Strongylodon lucidus. Then, in a small opening above the trail is the amazing arborescent amaranth, Charpentiera abovata (papala) and, a little farther on, a tree of Osmanthus sandwicensis on the right, closely associated with *Citharexylum spinosum which is not spiny and, when sterile, is almost indistinguishable from Osmanthus, though one is in the Verbenaceae and the other in the Oleaceae.
Around a sharp turn to the left is mixed forest of koa, lehua, Hibiscus and guava, then, around a curve, one of the remarkable Hawaiian lobeliads, Cyanea angustifolia, above the trail. Beyond this, at a small bridge in a guava thicket, some small Pisonia sandwicensis (aulu) saplings, then koa forest with an understory of Hibiscus, Perrottetia, Euphorbia, Gouldia Psychotria #Cordyline and *Persea. On an open slope are #Cordyline, lehua and other bushes, much *Eupatorium riparium and, at the far end, a little *E. adenophorum (Mail pamakani) . Then the trail goes for a distance through guava thickets with some native plants including Myrsine lessertiana and with considerable #Cordyline. Then there are several small banana plants and Touchardia latifolia (olona) on the left. Touchardia is an endemic Hawaiian genus of Urticaceae with one of the strongest fibers known, used by the old Hawaiians for fish nets and lines, and especially for the backing of their famous feather cloaks. The rocks above the trail are covered by ferns, including *Adiantum cuneatum, and Tectaria gaudichaudii, with Selaginella menziesii and a large hepatic. Embelia paciflca is the liana hanging over the trail. It may be identified by the black flecks in its leaves, seen when they are held up to the light.
In a wide ravine are Touchardia, #Muse sapientum, #Cordyline *Coix lachrymajobi, #Colocasia esculenta (taro) and Cyrtandra cf. cordifolia. Judging by the presence of certain of these species it seems likely that this ravine was the site of old Hawaiian cultivation. The bananas and taro, at least, did not likely get here without the aid of man.
Along the trail, beyond some guava forest, is an opening with Freycinetia, *Ipomoca alba (moon flower) and Clermontia kokeana, another of the famous Hawaiian lobeliads. This is at the base of a large koa, with more of the same beyond on the right, and Ilex anomala on the left above the trail. Open koa wood with much Freycinetia and Hibiscus arnottianus occupies much of this area. A large Pisonia sandwicensis (aura) may be seen on a small ridge top to the left. From here in, there is more lehua than koa, and the vegetation may be regarded as lehua forest, rather than the koa forest which has prevailed, though not very well preserved, so far. An open slope provides another magnificent view of Manoa Valley and the mountains with conspicuous light green kukui patches and the planted forest of the Manoa Arboretum in the bottom of the valley head below. The amphitheaterlike character of this valley can be seen very well from here.
The trail skirts brushy cliffs with lehua and Hibiscus, and both species of *Eupatorium, to a small patch of mixed wood, with koa, lehua, Hibiscus, Antidesma, #Cordyline and *Citharexylum. It goes around a sharp curve and down a small slope. A dead koa on the right supports epiphytic Nephrolepis exaltata and Clermontia kokeana. At the next small curve is a bush of the rare Oahu variety of Psychotria hexandra, known by its large membranous interpetiolar stipules, caducous as in somewhat similar American species. Through a *PsidiumHibiscus forest with Athyrium proliferum, into guavalehua forest and down a slope into a lehuakoa forest, the trail reveals rapid changes in vegetation. Here are Ilex anomala, Clermontia kakeana, Perrottetia sandwicensis, Gouldia terminalis, Antidesma platyphylla, Psychotria (Straussia), sp., and the introduced *Citharexylum spinosum, all common. Among the ferns here are Polypodium spectrum and Trichomanes davallioides.
Here is the intersection with the Tantalus Pauoa Flats trail. The left fork leads to the top of Tantalus, a branch of it to the right going around the side of Tantalus, and the right fork down and across Pauoa Flats to the edge of Nuuanu Valley and up to the rain gauge at the head of Pauoa Flats.
The party can separate here, those who are a bit tired crossing and going straight ahead; those still good for a brisk walk of an extra mile may turn to the right and start down hill. Following the trail down an eroded slope, this party will see several Pisonia trees. On the flat below is a planted forest of several species of * Ficus, several of *Eucalyptus including *E. robusta, *Melaleuca quinouenodia, *Lagerstroemia speciosa, and other trees set out by the foresters perhaps 30 years ago. There is a large patch of bamboo, also planted, and then guava forest almost all the way to a small gap overlooking Nuuanu Valley. On a sharp ridge to the left are several native trees, including Gouldia terminalis, Pelea clusiaefolia, and several forms of Metrosideros collina. By this time it will have been noticed that many differentlooking trees go by this name. Continued attention to these is suggested. They form a complex that has so far defied adequate taxonomic treatment.
In the draw sloping toward Pauoa is a muddy grassland with *Panicum purpurascens, *Setaria Palmifolia, *Commelina diffuse and Ludwigia octovalvis.
The brushy slope opposite is covered by a heterogenous population of Metrosideros, with Wikstroemia cf. oahuensis, Scaevola gaudichaudiana and, at higher levela, Scaevola mollis. Years ago there was a swarm of hybrids between these two on this slope. Now they are so crowded by lehua trees that they are not very evident anymore.
Returning along the same trail, a right fork is taken at the foot of the hill, and the trail traverses a slope through guava forest until It rejoins the Tantalus Trail coming down from the upper slope of the mountain.
The party that takes the left fork at the Tantalus intersection, almost immediately comes to another intersection and takes the right fork (straight ahead). The left fork goes to the summit of Tantalus, covered by bamboo brake. The forest on the right fork is a koa with some guava, with *Eupatorium especially *E. adenophorum. very common, and some lehua. This changes very soon to almost pure guava forest with a ground cover of *Commelina diffuse and occasional patches of *Canna indica and *Coix lachrymajobi The trail descends through this by switchbacks. On the banks is *Blechnum occidentale and in the forest Nephrolepis exaltata (or N. cordifolia). Along the trail are outcrops of lava rock with moss, *Adiantum cuneatum and the tiny Trichomanes saxifragoides, one of the smallest of ferns. Patches of Hedychium sp. and Thelypteris dentata may be seen along the trail before it rejoins the trail from Pauoa Flats at about the 490 m contour.
On this trail on a large lava rock on the left are Peperomia reflexa, Polypodium thunbergianum and Trichomanes saxifragoides. Farther on *Adiantum cuneatum is abundant on these rocks, Then there is a sudden change in the rock exposed on the left side of the trail, from hard massive basaltic flow lava to ''black sand" or semiconsolidated lapillituff. Selaginella menziesii is common on this. A large draw is filled with *Aleurites (kukui) forest. Then on a straight stretch of trail, koa forest with some lehua, Elaeocarpus bifidus, Ilex anomala, Psychotria sp., Antidesma platyphylla, Perrottetia sandwicensis, Freycinetia arborea and other native plants in the lower layer. After a stretch of guava forest with *Persea americana and other planted trees in it, there are large kukui and various other trees, then thickets of coffee, *Coffee arabica, thoroughly naturalized here.
From here, guava forests on the ridges alternate with kukui forest in the draws. *Albizia falcataria is planted, Pipturus albldus, koa and lehua are native, scattered in the thickets, and large planted *Lagerstroemia speciosa, as well as *Eugenia jambos. From here are excellent views of Pauoa Valley, Honolulu Harbor, Pearl Harbor, and Barbers Point. On the last stretch of trail are many planted exotic trees, including *Persea, *Cryptomeria japonica, *Ficus of several species, *Acacia of several species, and where the trail reaches the road, Hibiscus tiliaceus. The buses will be waiting here.