Aluminum in Plants Moomaw et ah 
339 
in the Polypodiaceae and Cihotium chamissoi, 
contained very low levels of aluminum where 
they were encountered. 
Among the monocotyledons, the common, 
naturalized, wild orchid, Spathogkttis pUcata 
was found to have a sufficiently high alumi- 
num content in the leaves (3550 p.p.m.) to be 
classed as an accumulator but the single de- 
termination is considered insufficient for a 
firm decision. This is the first known positive 
report for orchids. 
The three positive finds for the grasses are 
thought to be especially interesting because 
of their involvement in the phosphorus me- 
tabolism of herbivores and because of nega- 
tive reports for 16 species by Webb (1945), 
and for the family in general by Hutchinson 
( 1943 ). Costin ( 1954 ) is the only known 
source of a positive graminaceous determina- 
tion. All three of the species of grasses with 
high aluminum are common in the native 
pastures on the acid soils of the high rainfall 
areas in Hawaii. Yellow foxtail {Setaria genicu- 
lata) was relatively low (1540 p.p.m.) for a 
single determination, but rattail grass {Sporo- 
bolus capensis) contained more than 5000 
p.p.m. in the Haiku area. Rice grass {Paspa- 
lum orhkulare) qualified as an accumulator in 
all three of the collection locations and shows 
a tendency toward increased aluminum con- 
tent with age as well as a wide range (1400- 
5970 p.p.m.). It should be pointed out that 
the accumulation of aluminum in a forage 
grass may account in part for the observed 
phosphate deficiency symptoms of cattle 
grazing in these areas since it has been shown 
(Hutchinson, 1943) that ingestion of alumi- 
num lowers phosphorus levels in blood, bone, 
and urine of several other animals. Hilo grass 
[Paspalum conjugatuwi) and fountain grass 
{Pennisetum ruppelit) were low in aluminum 
where they were collected and the introduced 
pangola grass {Digitaria decumbens) was very 
low. 
The dicotyledons of interest, other than 
Melastoma, are the dark-blue-fruited night- 
shade, or popolo, Solanum mdiflomm, which 
TABLE 2 
Aluminum Content, Dominant Soil Mineral, 
AND Classification of Hawaiian Soils from Which 
Plant Samples Were Taken 
SOIL 
SERIES 
great soil 
GROUP 
dominant 
SOIL 
MINERAL 
aluminum 
content 
(% AI2O3) 
Haiku 
Humic ferrugi- 
nous latosol 
Free oxides 
25-40 
Kapaa 
Aluminous fer- 
ruginous 
latosoi 
Free oxides 
40-60 
Kukaiau 
Humic latosoi 
Free oxides, 
amorphous 
minerals 
20-35 
Honokaa 
Hydrol humic 
latosoi 
Free oxides, 
amorphous 
minerals 
15-30 
was high (3850 p.p.m.) in aluminum, and 
Japanese tea {Cassia leschenaultiana) , which 
was positive on Maui but not on Kauai. The 
widespread and remarkably adaptable ohia 
lehua {Metrosideros collina subsp. polymorpha) 
was very low, as was the closely related 
Macadamia nut (a member of the Proteaceae) . 
These two plants and pangola grass show 
such low levels of aluminum that a metabolic 
device for excluding aluminum seems proba- 
ble, Rhodomyrtus contains a slightly low level 
but guava {Psidium guajava) maintains a con- 
sistently "average” value even on soils varying 
widely in aluminum content (Table 2). Al- 
though a more intensive sampling program 
may reveal more members of these categories 
as well as more samples of an intermediate 
nature, it seems reasonable to classify the 
plants sampled ™all caldfugous species grow- 
ing on soils of low pH, and highly leached 
root zones — into the following categories: 
1. Plants that exclude aluminum to some 
degree 
2. Plants that take up aluminum 
Facultative accumulators 
Obligate accumulators 
3. Plants indifferent to aluminum in the 
substrate 
Supporting physiological evidence is needed 
