SAGO PALM 28-2:35−48 (2020)

Phytolith Assemblages in Sago Palm (Rottb.) Leaflets

Masanori Okazaki1, Mitsuhisa Baba2, Toshihiko Momose3,
Marcelo A. Quevedo4 and Ma. Kristine L. Aban4
1

Japan Soil Research Institute, Inc., 3-26-4, Yatocho, Nishitokyo, Tokyo 188-0001 Japan
Kitasato University, 35-1, Higashinijusanbanncho, Towada, Aomori 034-8628 Japan

2

Ishikawa Prefectural University, 1-308, Suematsu, Nonoichi, Ishikawa 921-8836 Japan

3
4

Philippine Rootcrops Research and Training Center (PhilRootcrops), Visayas State University, Leyte, Philippines

Abstract: Phytolith (biogenic opal silica) assemblages in all organs of the palm family are formed by the uptakeof silicon from the soil through the root system. Characteristic Metroxylon sagu phytoliths were counted toevaluate their presence and size distribution in different leaf and leaflet positions at the approaching flowering
stage. At the sago field in Pangasugan, Leyte, Philippines, the samples of M. sagu were collected from upper (the4th leaf from the apex), middle (the 8th), and lower (the 11th or 14th) leaf portion and from upper, middle andlower leaflet position of each leaf. Phytolith assemblages in M. sagu leaflets were extracted by a dry combustion
method with an electric furnace and described based on morphology and ornamentation according toInternational Code for Phytolith Nomenclature 1.0 and 2.0 using a light-transmitting and scanning electron
microscope. Spheroid echinate phytoliths, which were highly diagnostic with minor exceptions, were observedin the leaflets of M. sagu (three palms) in Pangasugan. Incinerated leaflet samples amounted to approximately
9% of the oven-dry weight of leaflet. The phytoliths were counted under a light-transmitting microscope. The
mean diameter of phytoliths was 13.2 μm. Phytoliths were divided into five classes by diameter size; <5 (A), 5–
10 (B), 10–15(C), 15–20 (D), and >20 μm (E) accounted for 11.3, 23.4, 23.5, 25.9,and 15.9% of the total
phytoliths, respectively. The number of conical projections (spines) in the five classes ranged from 8 to 34 with amean value of 24.8. The largest number of spines (more than 30) was found in 15–20 μm (D) and >20μm (E)phytoliths. The increasing trend of the mean number of spines was observed in the increasing diameter ofphytoliths with some exceptions. The phytolith assemblages supplied by M. sagu will contribute to an usefulindicator of M. sagu growth for vegetation reconstruction and archaeological study.
Keywords: echinate, Philippines, silicon, spheroid, spine

Silicon (Si) is a beneficial element for plants and isincreases the phytolith content of rice plants to 5 to 6%

present in soil solution as Si(OH)4 (Currie and Perry,(Kondo, 2010; Sun et al., 2019). Si has positive effects

2007; Nawaz et al., 2019). It alleviates the toxic effects

on the breaking resistance and bending moment of ricecaused by stresses of heavy metals, salt, and drought(Fallah, 2012), resulting in a sufficient supply of Si(Ma, 2004). The vigor of plants is assisted by Sithat provides stability for culms and serves to decrease(Luyckx et al., 2017). Both monocotyledons andthe risk of lodging for rice plants.

dicotyledons produce phytoliths (Kealhofer and

Plants can absorb Si with radial and passive

Piperno, 1998; Huisman et al., 2018). Si depositiontransport from external solution (Mitani and Ma,

increases the abrasiveness of plant tissue and reduces

2005). Si dissolved from rocks and minerals in soil is

its palatability and digestibility for herbivores (Masseytransported to the surface of the rice root by mass flow

and Hartley, 2009). The uptake of Si significantly

and is absorbed through root cells to vessels by three

36

M. Okazaki et al.

kinds of Si transporters (Lsi1, Lsi2, and Lsi6) (Ma andis remarkable; Arecaceae phytoliths were larger than

Yamaji, 2006; Mitani et al., 2009). Silicon in the soil

those of Bromeliaceae. The ornamented globularsolution is taken up to the inside of exodermis cells byphytolith is considered a reliable indicator of palms.

Lsi1. Lsi2 can transport Si from the inside of

Szczepanowska (2018) provided images of rattan

exodermis cells to outside the cells (the apoplast(Calameae Kunth) phytoliths in parenchyma fibers

pathway). In endodermis cells, Si is again transported

using a scanning electron microscope and the element

to the cortex by the working of Lsi1 and Lsi2. Finally,in phytoliths using energy-dispersive X-ray

Si flows through vessels to aboveground byspectroscopy (EDX).

transpiration flow. Lsi6 plays a role in the unloading of

However, there are few reports of phytolith

Si in the xylem parenchyma adjacent to the phloem offormation in M. sagu (Fenwick et al., 2011; Bowdery.

the leaf blade and sheath (Yamaji et al., 2008).

2014). Fenwick et al. (2011) showed that theMorphometric analysis allows researchers toassemblage-based approach of M. sagu phytoliths

classify the entire palm family (Delhon and Orliac,

provided potential value for archaeological analysis.

2007). Patterer (2014) described phytoliths of the main

Likewise, Bowdery (2014) found higher percentages ofpalm species (Arecaceae) present in the subtropicalM. sagu phytoliths at a depth of 0.97 m in the Rano

regions of South America. Satakentia and Arenga

Kau (Easter Island, Chile) core sample, which

phytoliths were found to be 1.84 and 6.87%,

corresponded to AD 1634–1672 based on 14C dating,respectively, of the total dry weight (Kondo, 2010).

than those at other layers. Recently, Baba et al. (2020)

Arecaceae produces large amounts of phytoliths andelucidated M. sagu phytolith assemblages in the 6th

has globular echinate morphotypes in its tissueleaf from the apex in Pangasugan, Leyte, Philippines.

(Delhon and Orliac, 2007; Kondo, 2010; Benvenuto etHowever, they did not describe the phytolithal., 2015). The features of globular morphology amongassemblages of different leaves and leaflets. This study

Arecaceae, Bromeliaceae, Cannaceae, Marantaceae,

used the characteristics of M. sagu phytoliths - spheroid

Orchidaceae, Strelitziaceae, and Zingiberaceae were

echinate shape, 13.2 μm of the mean diameter, 26.0 of

distinguished. Arecaceae is a large family of abundant

the mean number of conical projections (spines), 84.0 °phytolith producers. The small globular bodies (10–15of the mean terminal angle, and 0.54 μm of the mean

μm in diameter) in the various phytolith morphologies

length of conical projections (spines) under light-

are of particular use for diagnostic and identificationtransmitting microscope presented by Baba et al.

purposes. A continuum of surface ornamentation was(2020) and Okazaki et al. (2020).

displayed on these bodies, varying from psilate to

The objectives of this study were to describe thetuberculate, with echinate nodes being the mostmorphological characteristics (spheroid echinate) ofcommonly observed surface feature. Members ofphytoliths in M.sagu leaflets and to show the size

Palmae produce two types of phytoliths: hat-shaped or

distribution, number of spines, and spine length of M.

conical forms with flat bases, and irregular sphericalsagu phytoliths in leaflets in accordance with theforms; both types usually have rough, spinulose

International Code for Phytolith Nomenclature 1.0

surfaces (Tomlinson, 1969). Piperno (1988) noted that

(Madella et al., 2005) and 2.0 (Neumann et al., 2019).

Palmae species were common to abundant producers
of distinctive spherical phytoliths with echinate toMaterials and Methods

tuberculate surface ornamentation. The ornamented

Phytoliths in sago palm leaflets

globular bodies produced in the Arecaceae overlap

Three M. sagu (Palms Y, R, and W) were felled forsome with those of Bromeliaceae (Tomlinson, 1969;leaf sampling; palm heights were 11.9, 11.7, and 11.1

Piperno, 1988). The size differential between families

m, respectively, just before the flowering stage inPhytolith Assemblages in Sago Palm (Metroxylon sagu Rottb.) Leaflets

37

Table 1. Growth factors of three palms in Pangasugan, Leyte, Philippines

Pangasugan, Leyte, Philippines (Table 1). Of the threepalms, Palm W was the most severely damaged by
Typhoon Yolanda in 2015 (Okazaki et al., 2013). M.
sagu leaf samples (Fig. 1) of the 4th, 8th, and 11th or

1

4
5

2
6
3
Leaf position

Leaflet position

Fig. 2. Simplified diagram of Metroxylon sagu leaves and leaflets

Fig 2. Simplified diagram of Metroxylon sagu leaves and leaflets
1: upper leaf; 2: middle leaf; 3: lower leaf;
4: upper leaflet; 5: middle leaflet; 6: lower leaflet

with distilled water three times. Eight hours after
shaking, the top 10 cm of supernatant was removed
Fig. Metroxylonsagu
1. Metroxylon sagu leaves
in Pangasugan, Leyte,
Philippines,
Fig 1.
leaf inPangasugan,
Leyte,
Philippines
in 2019(2019)

from the water in a test tube. The phytolith samples in
the remaining solution were centrifuged and dried in adrying oven at 105 ℃. Matsunami MGK-S embedding

14th leaf from the apex were collected from theexperimental sago field of Pangasugan in 2019. Leaf
samples were divided into three positions: upper,
middle, and lower. Furthermore, leaflet samples weredivided into three positions of different leaves: upper,
middle, and lower and air-dried after washing with
distilled water (Fig. 2). About 21 g of fresh leaflet
samples was oven-dried at 105 ℃ and incinerated inan electric furnace at 500℃ for 4 hours. Incinerated
leaflet samples were weighed. Parts of the incinerated
samples were rinsed in 0.01 mol/L HCl and washedagent (polystyrene) was used for mounting andcovered with a cover glass for observation under alight-transmitting microscope (LTM) (Meiji Techno
MT5000) at 100x and 400x magnification in order tocount the small to large phytoliths, although Albert etal. (2009) and Katz et al. (2010) proposed a method ofsolution separation involving a sequential procedure ofsieving, acid digestion, and sodium polytungstate(Na6(H2W12O40)·H2O). The phytolith samples werestored individually in small vials. The presence ofphytoliths was recorded according to the description of

M. Okazaki et al.

38

the International Code for Phytolith Nomenclature 1.0(Madella et al., 2005) and 2.0 (Neumann et al., 2019):
3D shape, 2D shape, texture, and ornamentation. The

Table 2. Dry weight percent of incinerated leaflet samples
in different leaves and leaflets of three Metroxylon
sagu

maximum diameter from spine (conical projection) tip
to spine tip (the phytolith’s largest visible dimension)and the number of spines were determined. A total of
20 to 70 phytoliths was counted per sample to quantify
the relative abundances of morphotypes (Albert et al.,2009). Around 30 phytoliths were measured to obtainthe size distribution of 5 classes by diameter size: <5,
5–10, 10–15, 15–20, and >20 μm. The percentage ofdifferent sizes of M. sagu phytoliths was calculated asa reference from the results of Yong et al. (2010). The
total numbers of M. sagu leaflet spines were counted
under LTM (Fig. 3) and multiplied by two. A scanningelectron microscope (SEM) (Hitachi Miniscope TM1000) was used to confirm the morphological featuresof dried samples, angles, and lengths of spines without
any special pretreatment.

0

10 m

Fig. 3. Spines on the surface of a M. sagu phytolithFig 3. Open
Spineson theof an
M.numbersagu phytolith
circlesshowsurface
spines. The
total
of spines is calculatedOpen
circlesshow
the spines
on thefront.spines. The total number of spines
is calculated by doubling the spines on the front.

Results
1. Phytoliths in different leaf positions ofMetroxylon sagu
Silicon uptake by M. sagu resulted in the formationof spheroid echinate phytoliths. The mean incinerated
leaflet samples amounted
to 9.0 ± 4.9% of the total
leaflet dry weight (Table

YMm2). The phytoliths in theleaflet epidermis of M.

YMm
0 10 

sagu were observed under
microscope (Figs. 4 to 6).
With several exceptions,they presented 20 to 30

RMm

sagupphytoliths
FigFig. 4. 4.MMetroxylon
etro
oxxyl
x on sagu
hytoliths in
in incinerated
in
ncinerated leafletspines symmetricallyleaflet samples from Pangasugan,
samp
le
e
s
f
r
o
m
P
an
g
as
u
g
an
,
L
e
y
t
e, Philippines in
Leyte, Philippines in 2019
arranged at the periphery,
2019
YMm: Palm Y, middle leaf, middle leaflet
YM
m
:
P
alm
Y,, R,
middle leleaf,
aff,, middlle leleaflet
aflet
RMm: PalmY
middlemiddlewhich agreed with the
WMm:
Palm
middlemiddleleafletRM
m: Palm
R,W,
mid
dle leleaf,
aff,, middle leaflet

WMm: Palm W
W,, middle leaff,, mid
ddle leaflet

observation of Okazaki etal. (2020). Phytoliths

serve as one diagnostic
WMmfeature that distinguishesPhytolith Assemblages in Sago Palm (Metroxylon sagu Rottb.) Leaflets

39
palms at the genus level(Kealhofer and Piperno,
1998; Prychid et al.,
2003; Piperno, 2006).

RMu

In Figs. 4 and 5, theRMuphytoliths in the leaflet

0 10 

tissue were distributed inrows, and slightly larger
phytoliths than thoseobserved in the field of

RMm

Fig 5. Metroxylon sagu phytoliths in an incinerated
leaflet sample
view were located in thefrom Pangasugan, Leyte, Philippines in 2019
Fig. 5. RMu:
MetrooxxxylonR,sagu
phyleaf,
toliths in leaflet
ann incinerated lea peripheral part of the
PalmmiddleuppersampleePalm
fromangasuleaf,
ganmiddle, Leyte,leaflet
Philippines in 2stomata guard cells.
RMm:
R, Pmiddle
RMl:
RMu:Palm
PalmR,Rmiddle, middleleaf,
lealower
ff,, uppleaflet
er leaflet

RMm: Palm R, middle leaff,, middle leaflet
RMl: Paalm R, middle leaff,, lower lleaflet

RMl

Figure 6 shows diagnostic

globular echinate types(Madella et al., 2005;
Osterrieth et al., 2009) or

0 10 

spheroid echinate types(Neumann et al., 2019) ofA

different sizes. LTM and SEM images ofB

phytoliths in Fig. 6 clearly show a spheroid
echinate morphotype, which corresponds to
the results of Fenwick et al. (2011) and
Bowdery (2014).
The mean maximum diameter of M. sagu

0



0

leaflet phytoliths was 13.2 ± 1.8μm (Table

Fig 6. LTM (A)and SEM (B) images of phytoliths in M. sagu
Fig. 6. LLTTM (A)annd SEM (B) Images of Phytoliths in M. sagu

3). The distribution of different sizes of M.
sagu phytoliths in leaflets is shown in Fig. 7,
indicating 11.3, 23.4, 23.5, 25.9, and 15.9%
for <5 μm (A), 5–10 μm (B), 10–15 μm (C),

Table 3. Mean maximum diameter, number, angle, and length of spines of Metroxylon sagu
phytolith assemblage (LTM)M. Okazaki et al.

40

15–20 μm (D), and >20 μm (E),
11.3

15.9

B
C

23.4

25.9
23.5

< 5 

A
1
2
3

5-10 
10-15 D

4

15-20 E

5

> 20 

respectively. Upper leaf samples of threepalms contained (D) + (E) size phytolithassemblages as 40 to 50% of the total
number of phytoliths with some exceptions(Fig. 8). Meanwhile, (D) + (E) phytolithassemblages of middle and lower leaf
samples provided 20 to less than 50% withlarge variations (Figs. 9 and 10). Among

7. Different
size distributionsof phytoliths
in Pangasugan,
M. sagu leaflets
eFig
distributionsof phytoliths
in M. sagu
leaflets from
Leyte,
from Pangasugan, Leyte, Philippines (three palms)
ree palms)
Leaflet samples taken from the upper, middle, and lowers taken from the upper, middle and lower positions of the upper (4th),
positions of the upper (4th), middle (8th), and lower (11thnd lower (11th and 14th) leaves.
and 14th) leaves%.
Figures show %.

three M. sagu, the percentages of incinerated
leaflet weight to oven-dried leaflet weight
are shown in Table 2. The mean incinerated
leaflet weight was 9.0%, ranging from 7.7 to
10.7% among the three different palms, 4.9

100%
100

< 5 

80%
80

B

5-10 

60%
60

C

10-15 D

15-20 E

> 20 

%

A

40%
40
20%
20

00%

1
2
3
4
5
6
7
8
9
YUu
YUm
YUl
RUu
RUm
RUl
WUu
WUm
WUl

FigFig.
8. 8.
Percentage
of different
sizesof phytoliths
in theupper
leaf leaf
Percentage
of different
sizesof phytoliths
in theupper
YUu: Palm Y, upper leaf, upper leaflet; YUm: Palm Y, upper leaf, middle leaflet;
YUu:
Palm
Y, upperleaf,leaf,
upper
leaflet;YUm:
Palm
Y, upperleaf,leaf,
middleYUl:
Palm
Y, upperlower
leaflet;RUu:
Palm
R, upperupperleaflet;
leaflet;YUl:RUm:
Palm Palm
Y, upperleaf, lower
leaflet;leaflet;
RUu: Palmupper
leaf, upper
leaflet;R, upperleaf, middle
RUl:R,Palm
R, upperleaf, lower
leaflet;
RUm:
Palm
R, upperleaf,leaf,
middleleaflet;RUl:
PalmPalm
R, upperleaf, lower
leaflet;leaflet;
WUu:
Palm
W, upper
upper
leaflet;WUm:
W, upperleaf, middle
WUu:
Palm
W, upperleaf,leaf,
upper
leaflet;
WUm: Palm W, upper leaf, middle leaflet;
WUl:
Palm
W, upperlower
leaflet
WUl: Palm W upper leaf lower leaflet
100%

100

A

< 5 

80%

80

B

5-10 

60

C

10-15 D

15-20 E

> 20 

%

60%

40

40%
20%
20
0%

0

1
2
3
4
5
6 WMu
7
8
9
YMu
YMm
YMl
RMu
RMm
RMl
WMm
WMl

9. Percentage
of different
sizesof phytoliths
in the middle
Fig 9.Fig.
Percentage
of different
sizes ofphytoliths
in the middle
leaf leaf
YMu: Palm Y, middle leaf, upper leaflet; YMm: Palm Y, middle leaf, middle leaflet;
YMu: Palm Y, middle leaf, upper leaflet; YMm: Palm Y, middle leaf, middle leaflet;
YMl: Palm Y, middle leaf, lower leaflet; RMu: Palm R, middle leaf, upper leaflet;
YMl:RMm:
Palm Palm
Y, middle
leaf, lower
leaflet;leaflet;
RMu: RMl:
Palm Palm
R, middle
leaf, upper
leaflet;R, middle
leaf, middle
R, middle
leaf, lower
leaflet;RMm:
PalmPalm
R, middle
leaf,leaf,
middleleaflet;RMl:
PalmPalm
R, middle
leaf, leaf,
lowermiddle
leaflet;WMu:
W, middle
upper
leaflet;WMm:
W, middle
leaflet;
WMu:
Palm
W, W,
middleleaf,
upper
leaflet;WMl:
Palm
middleleaf,
lower
leafletWMm: Palm W, middle leaf, middle leaflet;
WMl: Palm W, middle leaf, lower leaflet

Phytolith Assemblages in Sago Palm (Metroxylon sagu Rottb.) Leaflets41

to 11.7% among different leaf positions, and 7.7 tothe case of middle leaflet samples, the (D) + (E)

10.7% among different leaflet positions. The lower

phytolith assemblages revealed 40 to 50% of the total

leaf position provided the lowest percentage ofphytolith assemblages, decreasing in order of upper,

phytolith content in M. sagu. The accumulation of

middle, and lower leaves except for Palm R (Fig. 12).

silicon actively proceeds in the early growth stage,

On the other hand, lower leaflet samples ranged fromand phytoliths may gradually grow larger.

30 to 50% with large fluctuations (Fig. 13). The
phytolith assemblages in M. sagu leaves were not

2. Phytoliths in different leaflet positions offormed uniformly. The mean oven-dried weight

Metroxylon sagu

percentage of phytoliths varied from 7.7 to 10.7% for

The (D) + (E) phytolith assemblages of upper

different leaflet positions (Table 2).

leaflet samples ranged from 20 to 50% (Fig. 11). In

100

100%

A

< 5 

B

5-10 

60%
60

C

10-15 

40%
40

D

15-20 

20
20%

E

> 20 

80

%

80%

00%

1
2
3
4
5
6
7
8
9
YLu
YLm
YLl
RLu
RLm
RLl
WLu
WLm
WLl

Fig 10.
of different
sizessizesof phytoliths
in theinlower
leaf leaf
Fig. Percentage
10. Percentage
of dierentof phytoliths
the lower
YLu: Palm Y, lower leaf, upper leaflet; YLm: Palm Y, lower leaf, middle leaflet;Y, lowerleaf, lower
leaflet;R, leaf,lowermiddle
leaf, upper
leaflet;YLu: YLl:
PalmPalmY, lowerleaf, upperleaet;
YLm: RLu:
Palm PalmY, lowerleaet;RLm:Y,Palm
lower
leaf,leaet;middle RLu:
leaflet;RLl:
lower
leaf,leaet;lower leaflet;
YLl: Palm
lowerR,leaf,
lower
Palm
R,PalmlowerR,leaf,
upper
lower
leaf,
upperleaet;leaflet;RLl:
WLm:
Palm
W, lower
middleleaflet;RLm:WLu:
Palm Palm,R, lowerleaf,
middlePalm
R, lowerleaf,leaf,
lower
leaet;W,leaf,lower
leaf, leaet;lower leaflet
WLu:WLl:
PalmPalm, lowerupper
WLm: Palm W, lower leaf, middle leaet;
WLl: Palm W, lower leaf, lower leaet

100
100%
100

A

< 5 

B

5-10 

C

10-15 

40%
40

D

15-20 

20
20%
20

E

> 20 

80
80%
80

%

60
60%
60

00%

1
2
3
4
5
6
7
8
9
YUu
YMu
YLu
RUu
RMu
RLu
WUu
WMu
WLu

Fig 11.
Percentage
of different
sizes of phytoliths in the upper leaflet
Fig. 11.
Percentage
of dierent
sizes of phytoliths in the upper leaetYUu: Palm Y, upper leaf, upper leaflet; YMu: Palm Y, middle leaf, upper leaflet;
YLu:
Palm
Y, lower
upper
leaflet;RUu:
Palm
R, upperleaf,
leaf,upper
upperleaet;leaflet;YUu:
PalY, upperleaf,leaf,
upper
leaet;YMu:Pal
Y, iddle
RMu:
R, middle
leaf, upper
leaflet;R, lower
upper
leaflet;YLu:
PalPalmY, lowerleaf, upperleaet;RUu:RLu:PalPalm
R, upperleaf,leaf,
upper
leaet;WUu:
Palm,
upper leaf,
WMu:
Palm W,
middleleaf,
leaf,upper
upperleaet;leaflet;RMu:
Pal
R, iddle
leaf,upper
upperleaflet;leaet;
RLu: Pal
R, lower
WLu:
Palm
W, lower
upper
leaflet
WUu:
Pal, upperleaf,leaf,
upper
leaet;
WMu: Pal W, iddle leaf, upper leaet;
WLu: Pal W, lower leaf, upper leaetM. Okazaki et al.

42
100
100%

%

80%
80
60%
60
40%
40
20%
20

00%

A

< 5 

B

5-10 

C

10-15 D

15-20 E

> 20 

1
2
3
4
5
6
7
8
9
YUm
YMm
YLm
RUm
RMm
RLm
WUm
WMm
WLm

Fig. Percentage
12. Percentage
of differentof phytoliths
the middle
Fig 12.
of different
sizes sizesof phytoliths
in theinmiddle
leafletleaflet
YUm:
Palm
Y,
upper
leaf,
middleleaflet;
YMm:
Palm
Y,
middleleaf, middle
leaflet;YUm: Palm Y, upper leaf, middle leaflet; YMm: Palm Y, middle leaf, middle
leaflet;
YLm:
Palm
Y,
lower
leaf,
middleleaflet;
RUm:
Palm
R,
upper
leaf,
middleleaflet;YLm: Palm Y, lower leaf, middle leaflet; RUm: Palm R, upper leaf, middle leaflet;R, middle
leaf, middle
leaflet;
RLm: Palm R, lower leaf, middle leaflet;
RMm:RMm:
Palm Palm
R, middle
leaf, middle
leaflet;
RLm: Palm R, lower leaf, middle leaflet;
WUm: Palm, upper leaf, middle leaflet; WMm: Palm W, middle leaf, middle leaflet;
WUm: Palm , upper leaf, middle leaflet; WMm: Palm W, middle leaf, middle leaflet;
WLm: Palm W, lower leaf, middle leaflet
WLm: Palm W, lower leaf, middle leaflet

100%
100

A

< 5 

B

5-10 

60%
60

C

10-15 

40%
40

D

15-20 E

> 20 

%

80%
80

20%
20
0%

0

1 YMl
2
5 RLl6 WUl
7 WMl
8 WLl
9
YUl
YLl3 RUl4 RMl

Fig. 13. Percentage
of sizesdifferent
sizes of phytoliths
in thelower leaflet
Fig 13. Percentage
of differentof phytoliths
in the lower
leafletYUl: Palm Y, upper leaf, lower leaflet; YMl: Palm Y, middle leaf, lower leaflet;
YUl:YLl:
PalmPalm
Y, upperleaf, lower
YMl: Palm
middlelower
Y, lowerleaf, leaflet;
lower leaflet;
RUl:Y,Palm
R,leaf,upper
leaf,leaflet;
lower leaflet;
YLl: RMl:
Palm Y,
lower
lower
Palm
R, upperleaf,lower
lowerleaf,
leaflet;Palm
R, leaf,
middleleaf,leaflet;
lowerRUl:
leaflet;
RLl:
Palm R,
lower leaflet;
RMl:WUl:
PalmPalm,
R, middle
lowerleaflet;PalmPalmR, lowerleaf, lower
upperleaf,
leaf,
lower
leaflet;RLl:
WMl:
W, middle
leaf,leaflet;
lower leaflet;
WUl:
PalmPalm, upper
WMl: Palm W, middle leaf, lower leaflet;
WLl:
W, leaf,lowerlower
leaf, leaflet;
lower leaflet
WLl: Palm W, lower leaf, lower leaflet

3. Mean maximum diameter, number, angle, andones. The angle and length of spines were 87.1 ±length of spines on Metroxylon sagu phytoliths

10.7° and 1.1 ± 0.4 μm, respectively, which showed

The mean maximum diameter of phytoliths is13.2 ±1.8 μm (Table 3), which is slightly smaller thanthat reported by Fenwick et al. (2011), who noted thethe intermediate values between the TLM and SEM
measurements of Okazaki et al. (2020).

maximum diameter of 14.1 μm for 50 phytoliths of a

Discussion

M. sagu reference specimen. The number of spines on

1. Phytolith sizes in Metroxylon sagu

M. sagu phytolith (Palm Y) varied from 8 to 34, witha mean value of 24.8± 3.7 (Figs. 14 and 15). The 15–20μm (D) and >20 μm (E) phytolith assemblages
have more spines than the <5 (A) and 5–10μm (B)The Si content in the soil varied from 53.5 to86.8% (mean: 70.6%) as SiO 2 (Bowen, 1979).
Generally, the Si concentration in a soil solution
ranges from 0.1 to 0.6 mmol/L (Epstein, 1994). Si

Phytolith Assemblages in Sago Palm (Metroxylon sagu Rottb.) Leaflets

43

mean number of spines

35
30
25
20
15
10
5
0

1
YUu

2
YUm

3
YUl

4
YMu

5
YMm

6
YMl

7
YLu

8
YLm

9
YLl

Mean number of spines

Mean number of spines

Mean number of spines

g. 14. Mean number of spines on the surface of phytoliths with different positions of
Fig 14.
numberspines on Leyte,
the surfaceof phytoliths with different
theMeanleaf (PalmY) inof
Pangasugan,
Philippines
positions of the leaf (Palm Y) in Pangasugan, Leyte, Philippines
showsstandard
deviation.
TheThebar barshows
the thestandard
deviation.
Y: Palm
upperleaf;
leaf;M:M:middle
middleleaf;
leaf;L:L:lower
lowerleaf;
leaf;
Y: Palm
Y; Y;U:U:upper
u: upperleaflet;m: middle
leaflet;u: upperleaflet;m: middle
leaflet;l: lower
leafletl: lower
leaflet3030

Upper leaflet

25

2020
15

1010
5

00
3030

<5
1

5-10 10-15 15-20 >20 
2

3

4

5

Middle leaflet

25

2020
15

1010
5

00
3035

<5
1

5-10 10-15 15-20 >20 
2

3

4

5

Lower leaflet

30

2025

Fig. 15. Mean number of spines on

20
15

1010
5

00

<5
1

5-10 10-15 15-20 >20 
2

3

4

5

Fig 15. Mean number of spines on phytoliths
phytoliths (Palm Y) with dif(Palm Y) with different leaflet positions inleaflet positions
Pangasu
Pangasugan,
Leyte,inPhilippines
Leyte,
PhilippinesThebar showsthe standard deviation.

The bar shows the standard deaccumulation has been found to a great extent, but not

Mercader et al., 2009; Kondo, 2010; Morcote-Rios et

exclusively, in monocotyledonous plants (Currie andal., 2016). M. sagu is also capable of taking up Si as

Perry, 2007). Plants can accumulate, store, andsilicic acid in pH ranges up to 9.8, finally forming

process Si to create mesoporous silica nanoparticles

phytoliths in leaves, petioles, and seeds. Fenwick et(Sun et al., 2014) and phytoliths (Huisman et al.,al. (2011) reported that M. sagu phytoliths were more2018). Palms form characteristic phytoliths (Kondo,

clearly distinguishable than those of Arecacatechu,

1977; Kondo and Sase, 1986; Barboni et al., 2007;

Cocos nucifera, and Calamusaruensis, in order toM. Okazaki et al.

44

have a large mean diameter of 14.09 μm, a strong

3. Relationship between phytoliths and the breaking

tendency to be spherical (93.6% of the assemblage),resistance/bending moment in Metroxylon sagu

and a weak tendency toward having right-angled
spines (58.8% of the assemblage). However, theresults with respect to diameter in this study were
smaller than those of Fenwick et al. (2011) because ofdifferent portions of leaves and leaflets and different

Silicified cells in rice provide the much-needed
strength to resist culm breaking (Dorairaj and Ismail,2017). Fallah (2012) showed that the breaking
resistance of rice plants increased with increasing Si
content. Hossain and Choudhury (1975) also revealed

extraction methods used.

that added silicon under hydroponic culture

2. Description of Metroxylon sagu phytoliths for

Okazaki et al. (2013) reported the breaking resistancesignificantly increased the rigidity of rice stalks.

further studyof M. sagu leaflets. However, there has not yet been a

The morphometrical analysis of palm phytoliths

report on the relationship between phytolith content inshows important variations of size and shapeparameters from one species to another and from one
organ to another (Delhon and Orliac, 2007). The

cells of M. sagu and breaking resistance. The strong
breaking resistance of M. sagu might be dependent on
the array of phytoliths.

International Working Group on Phytolith
Nomenclature (IWGPN) developed a description ofphytoliths because standardizing and harmonizing thenames and descriptions of phytoliths would improve
communication between researchers and facilitate thecomparison of phytolith types and analyses (Madella
et al., 2005). The International Code for Phytolith
Nomenclature 1.0 presented by Madella et al. (2005)
and the International Code for Phytolith Nomenclature
2.0 (Neumann et al., 2019) are appropriately accepted
worldwide. The characteristic information ofphytoliths should be supplied in the order of shape,
texture/ornamentation,

symmetric

features,morphometric data, illustrations, and anatomical
origin. Palms produce two types of diagnostic
phytoliths. One type is a globular (spheroid) echinate
morph. The other type is a hemispherical or conicalhat-shaped rimmed morph, whose distribution isrestricted to Caryota, Orania, and Arenga. M. sagu
phytoliths are composed of globular or ellipsoidmorphs with a mean diameter of 14.086 μm, and they
exhibit regular echinate to nodulose surface
decorations (Fenwick et al., 2011). Almost all M. sagu
phytoliths are spheroid echinates, which are diagnostic
and can be definitively distinguished from other
Arecaceae phytoliths.

4. Metroxylon sagu phytoliths for past vegetation
reconstruction
Plants accumulate Si up to 0.1 to 10% on a dryweight base as biogenic silica phytoliths and provide
phytolith assemblage to soil (Currie and Perry, 2007).
Morcote-Rios et al. (2016) used phytoliths as a tool forarchaeobotany, palaeobotany, and palaeoecology,
reconstructing ancient floras and landscapes andinterpreting events in plant evolution and documenting
plant use by ancient peoples. Huisman et al. (2018)
also concluded that the analysis of phytoliths could
track local-scale vegetation dynamics, whereas pollen,
which was commonly used in palaeoecologicalreconstructions, reflected regional-scale vegetation
change. Lu and Liu (2005) reveled phytolithassemblages as indicators of coastal environmental
changes and hurricane overwash deposition.
Silicon uptake by M. sagu resulted in theaccumulation and formation of phytoliths in leaves,roots, and seeds. Bowdery (2014) reported thespherical echinate (globular echinate: International
Code for Phytolith Nomenclature) form of phytolith in
M. sagu to compare and classify the vegetation on the
remote southern oceanic island of Rapa Nui (Easter
Island) and, based on 14C dating, concluded that M.
sagu was present from AD 1425 to 1634 on EasterPhytolith Assemblages in Sago Palm (Metroxylon sagu Rottb.) Leaflets

45

Island in the southeast Pacific Ocean. This makes M.

Recently, multiple studies have revealed that thesagu a relative newcomer, as compared to Metroxylon

occluded carbon in phytoliths may play a role invitiense.

atmospheric carbon dioxide sequestration and climate

The Si-stable isotope composition of phytoliths waschange mitigation (Parr et al., 2010; Song, et al.,a good tool for elucidating paleoenvironmental

2014; Zuo et al., 2014). However, the fluxes of carbon

information. During the uptake and conversion ofin phytoliths from vegetation to soil and the residence

silicic acid into particulate hydrous silica, the lighter

time of carbon in phytoliths in soil are not clear

Si is preferentially incorporated into the silica over(Alexandre et al., 2015). We hope that we are able tothe heavier Si and Si (Leng et al., 2009), resulting

discover when Leyte Island started to cultivate M.

in phytoliths with lighter specific density than those ofsagu and expanded to the east and west coastal sides

quartz and opal. The element composition of riceof Leyte and why the east Leyte areas still have M.

phytoliths was determined by Li et al. (2014).

sagu and the west coastal side of Leyte has lost M.

Phytoliths have carbon of 1 to 5 wt% (Jones andsagu in the present time.

28

29

30

Beavers, 1963), which was occluded within the
micrometric internal cavities (Alexandre et al., 2015).

5. Contribution of Metroxylon sagu phytoliths toThearchaeological research

13

C/ C (δ C) ratios of carbon occluded in
12

13

phytoliths express the paleoclimatic condition andPhytoliths are used in archaeology to study ancient

vegetation (Kelly et al., 1991). Alexandre et al. (2015)

plant remains and can provide insight into ancient

showed the phytolith structure and occluded thediet, non-food uses of plants, the spatialcarbon location using 3-D X-ray microscopy andarrangements of plant use and discard acrossnanoscale secondary ion mass spectrometry

settlements, agricultural practices, and the seasonality(NanoSIMS), concluding that two groups of organicof pre-agrarian site occupations (Ryan, 2014).

carbon were presented in the cavities of phytoliths;

Taxonomically identifiable phytoliths are produced

one was susceptible to rapid oxidation, and the otherby many plants. Diagnostic spheroid echinate forms

was continuously distributed in and protected by thecan be distinguished (Madella et al., 2005; Morcote-silica structure.

Rios et al., 2016; Huisman et al., 2018; Neumann et

Phytolith study is a common tool used by manyal., 2019; Yin et al., 2014). M. sagu phytolith

researchers to document vegetation changes andassemblages from soil layers in Southeast Asia anddisturbance patterns related to human settlement andSouth Pacific Islands and radiocarbon dating provide

plant exploitation (Horrocks and Wozniak, 2008;

the distribution ages when transported from the

Benvenuto et al., 2015), accompanied by phytolith 14C

center of sago growing areas, as well as its growing

dating (Piperno and Stothert, 2003). Wilding (1967)and environmental conditions.

and Wilding et al. (1967) showed that occluded
carbon was a suitable substrate for 14 C dating,Conclusion

although the 14C age of phytolith-occluded carbon

M. sagu can take up and accumulate silicon to form

increased directly with the combustion temperature

phytolith (biogenic opal silica) assemblage, which(up to 1100°C), resulting in age overestimations ofamounted to 9.0% of dry leaflet weight. The phytoliths

hundreds of years (Yin et al., 2014). Piperno andof M. sagu are spheroid echinate forms, indicating a

Stothert (2003) reported that Cucurbita (squash andcharacteristic feature of the palm family. The

gourd) phytolith carbon in southwest Ecuador wasformation of phytoliths might be determined by

identified as dating to 10,130 to 9320 C years ago

genetics and, accidentally, by the silicon concentration(about 12,000 to 10,000 calendar years ago).

in the xylem and phloem fluid. The mean diameter of14

M. Okazaki et al.

46

M. sagu phytoliths was 13.2±1.8 μm. From this result,

trees of Easter Island: New radiocarbon and

it is concluded that M. sagu phytoliths have sufficient

phytolith data. Conference: VII International

qualifications for vegetation reconstruction and are a

Conference of Easter Island and the Pacific, 97-110,

stable archaeological indicator.

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